diff --git a/tools/warn/warn_common.py b/tools/warn/warn_common.py
index 0c9d9ef..329f1e5 100755
--- a/tools/warn/warn_common.py
+++ b/tools/warn/warn_common.py
@@ -18,6 +18,8 @@
 Default is to output warnings in HTML tables grouped by warning severity.
 Use option --byproject to output tables grouped by source file projects.
 Use option --gencsv to output warning counts in CSV format.
+
+Default input file is build.log, which can be changed with the --log flag.
 """
 
 # List of important data structures and functions in this script.
@@ -36,13 +38,11 @@
 #   project_patterns[p]              re.compile(project_list[p][1])
 #   project_names[p]                 project_list[p][0]
 #   warning_messages     array of each warning message, without source url
+#   warning_links        array of each warning code search link; for 'chrome'
 #   warning_records      array of [idx to warn_patterns,
 #                                  idx to project_names,
-#                                  idx to warning_messages]
-#   android_root
-#   platform_version
-#   target_product
-#   target_variant
+#                                  idx to warning_messages,
+#                                  idx to warning_links]
 #   parse_input_file
 #
 # To emit html page of warning messages:
@@ -61,8 +61,9 @@
 #
 # New dynamic HTML page's static JavaScript data:
 #   Some data are copied from Python to JavaScript, to generate HTML elements.
-#   FlagURL                args.url
-#   FlagSeparator          args.separator
+#   FlagPlatform           flags.platform
+#   FlagURL                flags.url, used by 'android'
+#   FlagSeparator          flags.separator, used by 'android'
 #   SeverityColors:        list of colors for all severity levels
 #   SeverityHeaders:       list of headers for all severity levels
 #   SeverityColumnHeaders: list of column_headers for all severity levels
@@ -88,80 +89,67 @@
 import multiprocessing
 import os
 import re
-import signal
 import sys
 
 # pylint:disable=relative-beyond-top-level
-from . import cpp_warn_patterns
-from . import java_warn_patterns
-from . import make_warn_patterns
-from . import other_warn_patterns
-from . import tidy_warn_patterns
+from . import android_project_list
+from . import chrome_project_list
+from . import cpp_warn_patterns as cpp_patterns
+from . import java_warn_patterns as java_patterns
+from . import make_warn_patterns as make_patterns
+from . import other_warn_patterns as other_patterns
+from . import tidy_warn_patterns as tidy_patterns
 # pylint:disable=g-importing-member
-from .android_project_list import project_list
 from .severity import Severity
 
-parser = argparse.ArgumentParser(description='Convert a build log into HTML')
-parser.add_argument('--csvpath',
-                    help='Save CSV warning file to the passed absolute path',
-                    default=None)
-parser.add_argument('--gencsv',
-                    help='Generate a CSV file with number of various warnings',
-                    action='store_true',
-                    default=False)
-parser.add_argument('--byproject',
-                    help='Separate warnings in HTML output by project names',
-                    action='store_true',
-                    default=False)
-parser.add_argument('--url',
-                    help='Root URL of an Android source code tree prefixed '
-                    'before files in warnings')
-parser.add_argument('--separator',
-                    help='Separator between the end of a URL and the line '
-                    'number argument. e.g. #')
-parser.add_argument('--processes',
-                    type=int,
-                    default=multiprocessing.cpu_count(),
-                    help='Number of parallel processes to process warnings')
-parser.add_argument(dest='buildlog', metavar='build.log',
-                    help='Path to build.log file')
-args = parser.parse_args()
 
-warn_patterns = make_warn_patterns.warn_patterns
-warn_patterns.extend(cpp_warn_patterns.warn_patterns)
-warn_patterns.extend(java_warn_patterns.warn_patterns)
-warn_patterns.extend(tidy_warn_patterns.warn_patterns)
-warn_patterns.extend(other_warn_patterns.warn_patterns)
-
-project_patterns = []
-project_names = []
-warning_messages = []
-warning_records = []
+def parse_args(use_google3):
+  """Define and parse the args. Return the parse_args() result."""
+  parser = argparse.ArgumentParser(
+      description=__doc__, formatter_class=argparse.RawDescriptionHelpFormatter)
+  parser.add_argument('--capacitor_path', default='',
+                      help='Save capacitor warning file to the passed absolute'
+                      ' path')
+  # csvpath has a different naming than the above path because historically the
+  # original Android script used csvpath, so other scripts rely on it
+  parser.add_argument('--csvpath', default='',
+                      help='Save CSV warning file to the passed path')
+  parser.add_argument('--gencsv', action='store_true',
+                      help='Generate CSV file with number of various warnings')
+  parser.add_argument('--byproject', action='store_true',
+                      help='Separate warnings in HTML output by project names')
+  parser.add_argument('--url', default='',
+                      help='Root URL of an Android source code tree prefixed '
+                      'before files in warnings')
+  parser.add_argument('--separator', default='?l=',
+                      help='Separator between the end of a URL and the line '
+                      'number argument. e.g. #')
+  parser.add_argument('--processes', default=multiprocessing.cpu_count(),
+                      type=int,
+                      help='Number of parallel processes to process warnings')
+  # Old Android build scripts call warn.py without --platform,
+  # so the default platform is set to 'android'.
+  parser.add_argument('--platform', default='android',
+                      choices=['chrome', 'android'],
+                      help='Platform of the build log')
+  # Old Android build scripts call warn.py with only a build.log file path.
+  parser.add_argument('--log', help='Path to build log file')
+  parser.add_argument(dest='buildlog', metavar='build.log',
+                      default='build.log', nargs='?',
+                      help='Path to build.log file')
+  flags = parser.parse_args()
+  if not flags.log:
+    flags.log = flags.buildlog
+  if not use_google3 and not os.path.exists(flags.log):
+    sys.exit('Cannot find log file: ' + flags.log)
+  return flags
 
 
-def initialize_arrays():
-  """Complete global arrays before they are used."""
-  global project_names, project_patterns
-  project_names = [p[0] for p in project_list]
-  project_patterns = [re.compile(p[1]) for p in project_list]
-  for w in warn_patterns:
-    w['members'] = []
-    # Each warning pattern has a 'projects' dictionary, that
-    # maps a project name to number of warnings in that project.
-    w['projects'] = {}
+def get_project_names(project_list):
+  """Get project_names from project_list."""
+  return [p[0] for p in project_list]
 
 
-initialize_arrays()
-
-
-android_root = ''
-platform_version = 'unknown'
-target_product = 'unknown'
-target_variant = 'unknown'
-
-
-##### Data and functions to dump html file. ##################################
-
 html_head_scripts = """\
   <script type="text/javascript">
   function expand(id) {
@@ -211,11 +199,11 @@
   return '<font size="+2">' + param + '</font>'
 
 
-def dump_html_prologue(title, writer):
+def dump_html_prologue(title, writer, warn_patterns, project_names):
   writer('<html>\n<head>')
   writer('<title>' + title + '</title>')
   writer(html_head_scripts)
-  emit_stats_by_project(writer)
+  emit_stats_by_project(writer, warn_patterns, project_names)
   writer('</head>\n<body>')
   writer(html_big(title))
   writer('<p>')
@@ -225,36 +213,54 @@
   writer('</body>\n</head>\n</html>')
 
 
-def sort_warnings():
+def sort_warnings(warn_patterns):
   for i in warn_patterns:
     i['members'] = sorted(set(i['members']))
 
 
-def emit_stats_by_project(writer):
-  """Dump a google chart table of warnings per project and severity."""
-  # warnings[p][s] is number of warnings in project p of severity s.
+def create_warnings(warn_patterns, project_names):
+  """Creates warnings s.t.
+
+  warnings[p][s] is as specified in above docs.
+
+  Args:
+    warn_patterns: list of warning patterns for specified platform
+    project_names: list of project names
+
+  Returns:
+    2D warnings array where warnings[p][s] is # of warnings in project name p of
+    severity level s
+  """
   # pylint:disable=g-complex-comprehension
   warnings = {p: {s.value: 0 for s in Severity.levels} for p in project_names}
   for i in warn_patterns:
-    # pytype: disable=attribute-error
     s = i['severity'].value
-    # pytype: enable=attribute-error
     for p in i['projects']:
       warnings[p][s] += i['projects'][p]
+  return warnings
 
-  # total_by_project[p] is number of warnings in project p.
-  total_by_project = {
+
+def get_total_by_project(warnings, project_names):
+  """Returns dict, project as key and # warnings for that project as value."""
+  # pylint:disable=g-complex-comprehension
+  return {
       p: sum(warnings[p][s.value] for s in Severity.levels)
       for p in project_names
   }
 
-  # total_by_severity[s] is number of warnings of severity s.
-  total_by_severity = {
+
+def get_total_by_severity(warnings, project_names):
+  """Returns dict, severity as key and # warnings of that severity as value."""
+  # pylint:disable=g-complex-comprehension
+  return {
       s.value: sum(warnings[p][s.value] for p in project_names)
       for s in Severity.levels
   }
 
-  # emit table header
+
+def emit_table_header(total_by_severity):
+  """Returns list of HTML-formatted content for severity stats."""
+
   stats_header = ['Project']
   for s in Severity.levels:
     if total_by_severity[s.value]:
@@ -262,8 +268,25 @@
           '<span style=\'background-color:{}\'>{}</span>'.format(
               s.color, s.column_header))
   stats_header.append('TOTAL')
+  return stats_header
 
-  # emit a row of warning counts per project, skip no-warning projects
+
+def emit_row_counts_per_project(warnings, total_by_project, total_by_severity,
+                                project_names):
+  """Returns total project warnings and row of stats for each project.
+
+  Args:
+    warnings: output of create_warnings(warn_patterns, project_names)
+    total_by_project: output of get_total_by_project(project_names)
+    total_by_severity: output of get_total_by_severity(project_names)
+    project_names: list of project names
+
+  Returns:
+    total_all_projects, the total number of warnings over all projects
+    stats_rows, a 2d list where each row is [Project Name, <severity counts>,
+    total # warnings for this project]
+  """
+
   total_all_projects = 0
   stats_rows = []
   for p in project_names:
@@ -275,8 +298,21 @@
       one_row.append(total_by_project[p])
       stats_rows.append(one_row)
       total_all_projects += total_by_project[p]
+  return total_all_projects, stats_rows
 
-  # emit a row of warning counts per severity
+
+def emit_row_counts_per_severity(total_by_severity, stats_header, stats_rows,
+                                 total_all_projects, writer):
+  """Emits stats_header and stats_rows as specified above.
+
+  Args:
+    total_by_severity: output of get_total_by_severity()
+    stats_header: output of emit_table_header()
+    stats_rows: output of emit_row_counts_per_project()
+    total_all_projects: output of emit_row_counts_per_project()
+    writer: writer returned by make_writer(output_stream)
+  """
+
   total_all_severities = 0
   one_row = ['<b>TOTAL</b>']
   for s in Severity.levels:
@@ -292,12 +328,26 @@
   writer('</script>')
 
 
-def dump_stats(writer):
+def emit_stats_by_project(writer, warn_patterns, project_names):
+  """Dump a google chart table of warnings per project and severity."""
+
+  warnings = create_warnings(warn_patterns, project_names)
+  total_by_project = get_total_by_project(warnings, project_names)
+  total_by_severity = get_total_by_severity(warnings, project_names)
+  stats_header = emit_table_header(total_by_severity)
+  total_all_projects, stats_rows = \
+    emit_row_counts_per_project(warnings, total_by_project, total_by_severity, project_names)
+  emit_row_counts_per_severity(total_by_severity, stats_header, stats_rows,
+                               total_all_projects, writer)
+
+
+def dump_stats(writer, warn_patterns):
   """Dump some stats about total number of warnings and such."""
+
   known = 0
   skipped = 0
   unknown = 0
-  sort_warnings()
+  sort_warnings(warn_patterns)
   for i in warn_patterns:
     if i['severity'] == Severity.UNMATCHED:
       unknown += len(i['members'])
@@ -344,7 +394,7 @@
   return patterns
 
 
-def dump_fixed(writer):
+def dump_fixed(writer, warn_patterns):
   """Show which warnings no longer occur."""
   anchor = 'fixed_warnings'
   mark = anchor + '_mark'
@@ -372,95 +422,156 @@
   writer('</blockquote>')
 
 
-def find_project_index(line):
-  for p in range(len(project_patterns)):
-    if project_patterns[p].match(line):
-      return p
+def write_severity(csvwriter, sev, kind, warn_patterns):
+  """Count warnings of given severity and write CSV entries to writer."""
+  total = 0
+  for pattern in warn_patterns:
+    if pattern['severity'] == sev and pattern['members']:
+      n = len(pattern['members'])
+      total += n
+      warning = kind + ': ' + (pattern['description'] or '?')
+      csvwriter.writerow([n, '', warning])
+      # print number of warnings for each project, ordered by project name
+      projects = sorted(pattern['projects'].keys())
+      for project in projects:
+        csvwriter.writerow([pattern['projects'][project], project, warning])
+  csvwriter.writerow([total, '', kind + ' warnings'])
+  return total
+
+
+def dump_csv(csvwriter, warn_patterns):
+  """Dump number of warnings in CSV format to writer."""
+  sort_warnings(warn_patterns)
+  total = 0
+  for s in Severity.levels:
+    total += write_severity(csvwriter, s, s.column_header, warn_patterns)
+  csvwriter.writerow([total, '', 'All warnings'])
+
+
+def find_project_index(line, project_patterns):
+  for i, p in enumerate(project_patterns):
+    if p.match(line):
+      return i
   return -1
 
 
-def classify_one_warning(line, results):
+def classify_one_warning(warning, link, results, project_patterns,
+                         warn_patterns):
   """Classify one warning line."""
-  for i in range(len(warn_patterns)):
-    w = warn_patterns[i]
+  for i, w in enumerate(warn_patterns):
     for cpat in w['compiled_patterns']:
-      # pytype: disable=attribute-error
-      if cpat.match(line):
-        p = find_project_index(line)
-        results.append([line, i, p])
+      if cpat.match(warning):
+        p = find_project_index(warning, project_patterns)
+        results.append([warning, link, i, p])
         return
       else:
         # If we end up here, there was a problem parsing the log
         # probably caused by 'make -j' mixing the output from
         # 2 or more concurrent compiles
         pass
-      # pytype: enable=attribute-error
 
 
-def classify_warnings(lines):
-  results = []
-  for line in lines:
-    classify_one_warning(line, results)
-  # After the main work, ignore all other signals to a child process,
-  # to avoid bad warning/error messages from the exit clean-up process.
-  if args.processes > 1:
-    signal.signal(signal.SIGTERM, lambda *args: sys.exit(-signal.SIGTERM))
-  return results
+def remove_prefix(s, sub):
+  """Remove everything before last occurrence of substring sub in string s."""
+  if sub in s:
+    inc_sub = s.rfind(sub)
+    return s[inc_sub:]
+  return s
 
 
-def parallel_classify_warnings(warning_lines, parallel_process):
-  """Classify all warning lines with num_cpu parallel processes."""
-  num_cpu = args.processes
-  if num_cpu > 1:
-    groups = [[] for x in range(num_cpu)]
-    i = 0
-    for x in warning_lines:
-      groups[i].append(x)
-      i = (i + 1) % num_cpu
-    group_results = parallel_process(num_cpu, classify_warnings, groups)
-  else:
-    group_results = [classify_warnings(warning_lines)]
+# TODO(emmavukelj): Don't have any generate_*_cs_link functions call
+# normalize_path a second time (the first time being in parse_input_file)
+def generate_cs_link(warning_line, flags, android_root=None):
+  if flags.platform == 'chrome':
+    return generate_chrome_cs_link(warning_line, flags)
+  if flags.platform == 'android':
+    return generate_android_cs_link(warning_line, flags, android_root)
+  return 'https://cs.corp.google.com/'
 
-  for result in group_results:
-    for line, pattern_idx, project_idx in result:
-      pattern = warn_patterns[pattern_idx]
-      pattern['members'].append(line)
-      message_idx = len(warning_messages)
-      warning_messages.append(line)
-      warning_records.append([pattern_idx, project_idx, message_idx])
-      pname = '???' if project_idx < 0 else project_names[project_idx]
-      # Count warnings by project.
-      if pname in pattern['projects']:
-        pattern['projects'][pname] += 1
-      else:
-        pattern['projects'][pname] = 1
+
+def generate_android_cs_link(warning_line, flags, android_root):
+  """Generate the code search link for a warning line in Android."""
+  # max_splits=2 -> only 3 items
+  raw_path, line_number_str, _ = warning_line.split(':', 2)
+  normalized_path = normalize_path(raw_path, flags, android_root)
+  if not flags.url:
+    return normalized_path
+  link_path = flags.url + '/' + normalized_path
+  if line_number_str.isdigit():
+    link_path += flags.separator + line_number_str
+  return link_path
+
+
+def generate_chrome_cs_link(warning_line, flags):
+  """Generate the code search link for a warning line in Chrome."""
+  split_line = warning_line.split(':')
+  raw_path = split_line[0]
+  normalized_path = normalize_path(raw_path, flags)
+  link_base = 'https://cs.chromium.org/'
+  link_add = 'chromium'
+  link_path = None
+
+  # Basically just going through a few specific directory cases and specifying
+  # the proper behavior for that case. This list of cases was accumulated
+  # through trial and error manually going through the warnings.
+  #
+  # This code pattern of using case-specific "if"s instead of "elif"s looks
+  # possibly accidental and mistaken but it is intentional because some paths
+  # fall under several cases (e.g. third_party/lib/nghttp2_frame.c) and for
+  # those we want the most specific case to be applied. If there is reliable
+  # knowledge of exactly where these occur, this could be changed to "elif"s
+  # but there is no reliable set of paths falling under multiple cases at the
+  # moment.
+  if '/src/third_party' in raw_path:
+    link_path = remove_prefix(raw_path, '/src/third_party/')
+  if '/chrome_root/src_internal/' in raw_path:
+    link_path = remove_prefix(raw_path, '/chrome_root/src_internal/')
+    link_path = link_path[len('/chrome_root'):]  # remove chrome_root
+  if '/chrome_root/src/' in raw_path:
+    link_path = remove_prefix(raw_path, '/chrome_root/src/')
+    link_path = link_path[len('/chrome_root'):]  # remove chrome_root
+  if '/libassistant/' in raw_path:
+    link_add = 'eureka_internal/chromium/src'
+    link_base = 'https://cs.corp.google.com/'  # internal data
+    link_path = remove_prefix(normalized_path, '/libassistant/')
+  if raw_path.startswith('gen/'):
+    link_path = '/src/out/Debug/gen/' + normalized_path
+  if '/gen/' in raw_path:
+    return '%s?q=file:%s' % (link_base, remove_prefix(normalized_path, '/gen/'))
+
+  if not link_path and (raw_path.startswith('src/') or
+                        raw_path.startswith('src_internal/')):
+    link_path = '/%s' % raw_path
+
+  if not link_path:  # can't find specific link, send a query
+    return '%s?q=file:%s' % (link_base, normalized_path)
+
+  line_number = int(split_line[1])
+  link = '%s%s%s?l=%d' % (link_base, link_add, link_path, line_number)
+  return link
 
 
 def find_warn_py_and_android_root(path):
-  """Set and return android_root path if it is found."""
-  global android_root
+  """Return android source root path if warn.py is found."""
   parts = path.split('/')
   for idx in reversed(range(2, len(parts))):
     root_path = '/'.join(parts[:idx])
     # Android root directory should contain this script.
     if os.path.exists(root_path + '/build/make/tools/warn.py'):
-      android_root = root_path
-      return True
-  return False
+      return root_path
+  return ''
 
 
-def find_android_root():
-  """Guess android_root from common prefix of file paths."""
+def find_android_root(buildlog):
+  """Guess android source root from common prefix of file paths."""
   # Use the longest common prefix of the absolute file paths
   # of the first 10000 warning messages as the android_root.
-  global android_root
-  warning_lines = set()
+  warning_lines = []
   warning_pattern = re.compile('^/[^ ]*/[^ ]*: warning: .*')
   count = 0
-  infile = io.open(args.buildlog, mode='r', encoding='utf-8')
-  for line in infile:
+  for line in buildlog:
     if warning_pattern.match(line):
-      warning_lines.add(line)
+      warning_lines.append(line)
       count += 1
       if count > 9999:
         break
@@ -468,56 +579,110 @@
       # the source tree root.
       if count < 100:
         path = os.path.normpath(re.sub(':.*$', '', line))
-        if find_warn_py_and_android_root(path):
-          return
+        android_root = find_warn_py_and_android_root(path)
+        if android_root:
+          return android_root
   # Do not use common prefix of a small number of paths.
   if count > 10:
     # pytype: disable=wrong-arg-types
     root_path = os.path.commonprefix(warning_lines)
     # pytype: enable=wrong-arg-types
     if len(root_path) > 2 and root_path[len(root_path) - 1] == '/':
-      android_root = root_path[:-1]
+      return root_path[:-1]
+  return ''
 
 
-def remove_android_root_prefix(path):
+def remove_android_root_prefix(path, android_root):
   """Remove android_root prefix from path if it is found."""
   if path.startswith(android_root):
     return path[1 + len(android_root):]
+  return path
+
+
+def normalize_path(path, flags, android_root=None):
+  """Normalize file path relative to src/ or src-internal/ directory."""
+  path = os.path.normpath(path)
+
+  if flags.platform == 'android':
+    if android_root:
+      return remove_android_root_prefix(path, android_root)
+    return path
+
+  # Remove known prefix of root path and normalize the suffix.
+  idx = path.find('chrome_root/')
+  if idx >= 0:
+    # remove chrome_root/, we want path relative to that
+    return path[idx + len('chrome_root/'):]
   else:
     return path
 
 
-def normalize_path(path):
-  """Normalize file path relative to android_root."""
-  # If path is not an absolute path, just normalize it.
-  path = os.path.normpath(path)
-  # Remove known prefix of root path and normalize the suffix.
-  if path[0] == '/' and android_root:
-    return remove_android_root_prefix(path)
-  return path
-
-
-def normalize_warning_line(line):
-  """Normalize file path relative to android_root in a warning line."""
-  # replace fancy quotes with plain ol' quotes
+def normalize_warning_line(line, flags, android_root=None):
+  """Normalize file path relative to src directory in a warning line."""
   line = re.sub(u'[\u2018\u2019]', '\'', line)
   # replace non-ASCII chars to spaces
   line = re.sub(u'[^\x00-\x7f]', ' ', line)
   line = line.strip()
   first_column = line.find(':')
-  if first_column > 0:
-    return normalize_path(line[:first_column]) + line[first_column:]
-  else:
-    return line
+  return normalize_path(line[:first_column], flags,
+                        android_root) + line[first_column:]
 
 
-def parse_input_file(infile):
-  """Parse input file, collect parameters and warning lines."""
-  global android_root
-  global platform_version
-  global target_product
-  global target_variant
-  line_counter = 0
+def parse_input_file_chrome(infile, flags):
+  """Parse Chrome input file, collect parameters and warning lines."""
+  platform_version = 'unknown'
+  board_name = 'unknown'
+  architecture = 'unknown'
+
+  # only handle warning lines of format 'file_path:line_no:col_no: warning: ...'
+  chrome_warning_pattern = r'^[^ ]*/[^ ]*:[0-9]+:[0-9]+: warning: .*'
+
+  warning_pattern = re.compile(chrome_warning_pattern)
+
+  # Collect all unique warning lines
+  # Remove the duplicated warnings save ~8% of time when parsing
+  # one typical build log than before
+  unique_warnings = dict()
+  for line in infile:
+    if warning_pattern.match(line):
+      normalized_line = normalize_warning_line(line, flags)
+      if normalized_line not in unique_warnings:
+        unique_warnings[normalized_line] = generate_cs_link(line, flags)
+    elif (platform_version == 'unknown' or board_name == 'unknown' or
+          architecture == 'unknown'):
+      m = re.match(r'.+Package:.+chromeos-base/chromeos-chrome-', line)
+      if m is not None:
+        platform_version = 'R' + line.split('chrome-')[1].split('_')[0]
+        continue
+      m = re.match(r'.+Source\sunpacked\sin\s(.+)', line)
+      if m is not None:
+        board_name = m.group(1).split('/')[2]
+        continue
+      m = re.match(r'.+USE:\s*([^\s]*).*', line)
+      if m is not None:
+        architecture = m.group(1)
+        continue
+
+  header_str = '%s - %s - %s' % (platform_version, board_name, architecture)
+  return unique_warnings, header_str
+
+
+def add_normalized_line_to_warnings(line, flags, android_root, unique_warnings):
+  """Parse/normalize path, updating warning line and add to warnings dict."""
+  normalized_line = normalize_warning_line(line, flags, android_root)
+  if normalized_line not in unique_warnings:
+    unique_warnings[normalized_line] = generate_cs_link(line, flags,
+                                                        android_root)
+  return unique_warnings
+
+
+def parse_input_file_android(infile, flags):
+  """Parse Android input file, collect parameters and warning lines."""
+  platform_version = 'unknown'
+  target_product = 'unknown'
+  target_variant = 'unknown'
+  android_root = find_android_root(infile)
+  infile.seek(0)
 
   # rustc warning messages have two lines that should be combined:
   #     warning: description
@@ -532,20 +697,25 @@
   warning_without_file = re.compile('^warning: .*')
   rustc_file_position = re.compile('^[ ]+--> [^ ]*/[^ ]*:[0-9]+:[0-9]+')
 
-  # Collect all warnings into the warning_lines set.
-  warning_lines = set()
+   # Collect all unique warning lines
+  # Remove the duplicated warnings save ~8% of time when parsing
+  # one typical build log than before
+  unique_warnings = dict()
+  line_counter = 0
   prev_warning = ''
   for line in infile:
     if prev_warning:
       if rustc_file_position.match(line):
         # must be a rustc warning, combine 2 lines into one warning
         line = line.strip().replace('--> ', '') + ': ' + prev_warning
-        warning_lines.add(normalize_warning_line(line))
+        unique_warnings = add_normalized_line_to_warnings(
+            line, flags, android_root, unique_warnings)
         prev_warning = ''
         continue
       # add prev_warning, and then process the current line
       prev_warning = 'unknown_source_file: ' + prev_warning
-      warning_lines.add(normalize_warning_line(prev_warning))
+      unique_warnings = add_normalized_line_to_warnings(
+          prev_warning, flags, android_root, unique_warnings)
       prev_warning = ''
 
     if warning_pattern.match(line):
@@ -553,7 +723,8 @@
         # save this line and combine it with the next line
         prev_warning = line
       else:
-        warning_lines.add(normalize_warning_line(line))
+        unique_warnings = add_normalized_line_to_warnings(
+            line, flags, android_root, unique_warnings)
       continue
 
     if line_counter < 100:
@@ -568,17 +739,36 @@
       m = re.search('(?<=^TARGET_BUILD_VARIANT=).*', line)
       if m is not None:
         target_variant = m.group(0)
-      m = re.search('.* TOP=([^ ]*) .*', line)
+      m = re.search('(?<=^TOP=).*', line)
       if m is not None:
         android_root = m.group(1)
-  return warning_lines
+
+  if android_root:
+    new_unique_warnings = dict()
+    for warning_line in unique_warnings:
+      normalized_line = normalize_warning_line(warning_line, flags,
+                                               android_root)
+      new_unique_warnings[normalized_line] = generate_android_cs_link(
+          warning_line, flags, android_root)
+    unique_warnings = new_unique_warnings
+
+  header_str = '%s - %s - %s' % (platform_version, target_product,
+                                 target_variant)
+  return unique_warnings, header_str
+
+
+def parse_input_file(infile, flags):
+  if flags.platform == 'chrome':
+    return parse_input_file_chrome(infile, flags)
+  if flags.platform == 'android':
+    return parse_input_file_android(infile, flags)
+  raise RuntimeError('parse_input_file not defined for platform %s' %
+                     flags.platform)
 
 
 # Return s with escaped backslash and quotation characters.
 def escape_string(s):
-  # pytype: disable=attribute-error
   return s.replace('\\', '\\\\').replace('"', '\\"')
-  # pytype: enable=attribute-error
 
 
 # Return s without trailing '\n' and escape the quotation characters.
@@ -589,19 +779,22 @@
   return escape_string(s)
 
 
-def emit_warning_array(name, writer):
+def emit_warning_array(name, writer, warn_patterns):
   writer('var warning_{} = ['.format(name))
-  for i in range(len(warn_patterns)):
-    writer('{},'.format(warn_patterns[i][name]))
+  for w in warn_patterns:
+    if name == 'severity':
+      writer('{},'.format(w[name].value))
+    else:
+      writer('{},'.format(w[name]))
   writer('];')
 
 
-def emit_warning_arrays(writer):
-  emit_warning_array('severity', writer)
+def emit_warning_arrays(writer, warn_patterns):
+  emit_warning_array('severity', writer, warn_patterns)
   writer('var warning_description = [')
-  for i in range(len(warn_patterns)):
-    if warn_patterns[i]['members']:
-      writer('"{}",'.format(escape_string(warn_patterns[i]['description'])))
+  for w in warn_patterns:
+    if w['members']:
+      writer('"{}",'.format(escape_string(w['description'])))
     else:
       writer('"",')  # no such warning
   writer('];')
@@ -621,7 +814,7 @@
     return byMessageCount(x1, x2);
   }
   const ParseLinePattern = /^([^ :]+):(\\d+):(.+)/;
-  function addURL(line) {
+  function addURL(line) { // used by Android
     if (FlagURL == "") return line;
     if (FlagSeparator == "") {
       return line.replace(ParseLinePattern,
@@ -631,6 +824,13 @@
       "<a target='_blank' href='" + FlagURL + "/$1" + FlagSeparator +
         "$2'>$1:$2</a>:$3");
   }
+  function addURLToLine(line, link) { // used by Chrome
+      let line_split = line.split(":");
+      let path = line_split.slice(0,3).join(":");
+      let msg = line_split.slice(3).join(":");
+      let html_link = `<a target="_blank" href="${link}">${path}</a>${msg}`;
+      return html_link;
+  }
   function createArrayOfDictionaries(n) {
     var result = [];
     for (var i=0; i<n; i++) result.push({});
@@ -690,10 +890,18 @@
                 "' style='display:none;'><table class='t1'>";
       var c = 0;
       messages.sort(compareMessages);
-      for (var i=0; i<messages.length; i++) {
-        result += "<tr><td class='c" + c + "'>" +
-                  addURL(WarningMessages[messages[i][2]]) + "</td></tr>";
-        c = 1 - c;
+      if (FlagPlatform == "chrome") {
+        for (var i=0; i<messages.length; i++) {
+          result += "<tr><td class='c" + c + "'>" +
+                    addURLToLine(WarningMessages[messages[i][2]], WarningLinks[messages[i][3]]) + "</td></tr>";
+          c = 1 - c;
+        }
+      } else {
+        for (var i=0; i<messages.length; i++) {
+          result += "<tr><td class='c" + c + "'>" +
+                    addURL(WarningMessages[messages[i][2]]) + "</td></tr>";
+          c = 1 - c;
+        }
       }
       result += "</table></div>";
     }
@@ -777,14 +985,14 @@
   writer('];')
 
 
-def emit_js_data(writer):
+def emit_js_data(writer, flags, warning_messages, warning_links,
+                 warning_records, warn_patterns, project_names):
   """Dump dynamic HTML page's static JavaScript data."""
-  emit_const_string('FlagURL',
-                    args.url if args.url else '', writer)
-  emit_const_string('FlagSeparator',
-                    args.separator if args.separator else '', writer)
-  emit_const_string_array('SeverityColors',
-                          [s.color for s in Severity.levels], writer)
+  emit_const_string('FlagPlatform', flags.platform, writer)
+  emit_const_string('FlagURL', flags.url, writer)
+  emit_const_string('FlagSeparator', flags.separator, writer)
+  emit_const_string_array('SeverityColors', [s.color for s in Severity.levels],
+                          writer)
   emit_const_string_array('SeverityHeaders',
                           [s.header for s in Severity.levels], writer)
   emit_const_string_array('SeverityColumnHeaders',
@@ -799,6 +1007,9 @@
                                writer)
   emit_const_html_string_array('WarningMessages', warning_messages, writer)
   emit_const_object_array('Warnings', warning_records, writer)
+  if flags.platform == 'chrome':
+    emit_const_html_string_array('WarningLinks', warning_links, writer)
+
 
 draw_table_javascript = """
 google.charts.load('current', {'packages':['table']});
@@ -822,82 +1033,201 @@
 """
 
 
-def dump_html(output_stream):
-  """Dump the html output to output_stream."""
+def dump_html(flags, output_stream, warning_messages, warning_links,
+              warning_records, header_str, warn_patterns, project_names):
+  """Dump the flags output to output_stream."""
   writer = make_writer(output_stream)
-  dump_html_prologue('Warnings for ' + platform_version + ' - ' +
-                     target_product + ' - ' + target_variant, writer)
-  dump_stats(writer)
+  dump_html_prologue('Warnings for ' + header_str, writer, warn_patterns,
+                     project_names)
+  dump_stats(writer, warn_patterns)
   writer('<br><div id="stats_table"></div><br>')
   writer('\n<script>')
-  emit_js_data(writer)
+  emit_js_data(writer, flags, warning_messages, warning_links, warning_records,
+               warn_patterns, project_names)
   writer(scripts_for_warning_groups)
   writer('</script>')
   emit_buttons(writer)
   # Warning messages are grouped by severities or project names.
   writer('<br><div id="warning_groups"></div>')
-  if args.byproject:
+  if flags.byproject:
     writer('<script>groupByProject();</script>')
   else:
     writer('<script>groupBySeverity();</script>')
-  dump_fixed(writer)
+  dump_fixed(writer, warn_patterns)
   dump_html_epilogue(writer)
 
 
-##### Functions to count warnings and dump csv file. #########################
+def parse_compiler_output(compiler_output):
+  """Parse compiler output for relevant info."""
+  split_output = compiler_output.split(':', 3)  # 3 = max splits
+  file_path = split_output[0]
+  line_number = int(split_output[1])
+  col_number = int(split_output[2].split(' ')[0])
+  warning_message = split_output[3]
+  return file_path, line_number, col_number, warning_message
 
 
-def description_for_csv(category):
-  if not category['description']:
-    return '?'
-  return category['description']
-
-
-def count_severity(writer, sev, kind):
-  """Count warnings of given severity."""
-  total = 0
-  for i in warn_patterns:
-    if i['severity'] == sev and i['members']:
-      n = len(i['members'])
-      total += n
-      warning = kind + ': ' + description_for_csv(i)
-      writer.writerow([n, '', warning])
-      # print number of warnings for each project, ordered by project name.
-      # pytype: disable=attribute-error
-      projects = sorted(i['projects'].keys())
-      # pytype: enable=attribute-error
-      for p in projects:
-        writer.writerow([i['projects'][p], p, warning])
-  writer.writerow([total, '', kind + ' warnings'])
-
-  return total
-
-
-# dump number of warnings in csv format to stdout
-def dump_csv(writer):
-  """Dump number of warnings in csv format to stdout."""
-  sort_warnings()
-  total = 0
-  for s in Severity.levels:
-    if s != Severity.SEVERITY_UNKNOWN:
-      total += count_severity(writer, s, s.column_header)
-  writer.writerow([total, '', 'All warnings'])
-
-
-def common_main(parallel_process):
-  """Real main function to classify warnings and generate .html file."""
-  find_android_root()
-  # We must use 'utf-8' codec to parse some non-ASCII code in warnings.
-  warning_lines = parse_input_file(
-      io.open(args.buildlog, mode='r', encoding='utf-8'))
-  parallel_classify_warnings(warning_lines, parallel_process)
-  # If a user pases a csv path, save the fileoutput to the path
-  # If the user also passed gencsv write the output to stdout
-  # If the user did not pass gencsv flag dump the html report to stdout.
-  if args.csvpath:
-    with open(args.csvpath, 'w') as f:
-      dump_csv(csv.writer(f, lineterminator='\n'))
-  if args.gencsv:
-    dump_csv(csv.writer(sys.stdout, lineterminator='\n'))
+def get_warn_patterns(platform):
+  """Get and initialize warn_patterns."""
+  warn_patterns = []
+  if platform == 'chrome':
+    warn_patterns = cpp_patterns.warn_patterns
+  elif platform == 'android':
+    warn_patterns = make_patterns.warn_patterns + cpp_patterns.warn_patterns + java_patterns.warn_patterns + tidy_patterns.warn_patterns + other_patterns.warn_patterns
   else:
-    dump_html(sys.stdout)
+    raise Exception('platform name %s is not valid' % platform)
+  for w in warn_patterns:
+    w['members'] = []
+    # Each warning pattern has a 'projects' dictionary, that
+    # maps a project name to number of warnings in that project.
+    w['projects'] = {}
+  return warn_patterns
+
+
+def get_project_list(platform):
+  """Return project list for appropriate platform."""
+  if platform == 'chrome':
+    return chrome_project_list.project_list
+  if platform == 'android':
+    return android_project_list.project_list
+  raise Exception('platform name %s is not valid' % platform)
+
+
+def parallel_classify_warnings(warning_data, args, project_names,
+                               project_patterns, warn_patterns,
+                               use_google3, create_launch_subprocs_fn,
+                               classify_warnings_fn):
+  """Classify all warning lines with num_cpu parallel processes."""
+  num_cpu = args.processes
+  group_results = []
+
+  if num_cpu > 1:
+    # set up parallel processing for this...
+    warning_groups = [[] for _ in range(num_cpu)]
+    i = 0
+    for warning, link in warning_data.items():
+      warning_groups[i].append((warning, link))
+      i = (i + 1) % num_cpu
+    arg_groups = [[] for _ in range(num_cpu)]
+    for i, group in enumerate(warning_groups):
+      arg_groups[i] = [{
+          'group': group,
+          'project_patterns': project_patterns,
+          'warn_patterns': warn_patterns,
+          'num_processes': num_cpu
+      }]
+
+    group_results = create_launch_subprocs_fn(num_cpu,
+                                              classify_warnings_fn,
+                                              arg_groups,
+                                              group_results)
+  else:
+    group_results = []
+    for warning, link in warning_data.items():
+      classify_one_warning(warning, link, group_results,
+                           project_patterns, warn_patterns)
+    group_results = [group_results]
+
+  warning_messages = []
+  warning_links = []
+  warning_records = []
+  if use_google3:
+    group_results = [group_results]
+  for group_result in group_results:
+    for result in group_result:
+      for line, link, pattern_idx, project_idx in result:
+        pattern = warn_patterns[pattern_idx]
+        pattern['members'].append(line)
+        message_idx = len(warning_messages)
+        warning_messages.append(line)
+        link_idx = len(warning_links)
+        warning_links.append(link)
+        warning_records.append([pattern_idx, project_idx, message_idx,
+                                link_idx])
+        pname = '???' if project_idx < 0 else project_names[project_idx]
+        # Count warnings by project.
+        if pname in pattern['projects']:
+          pattern['projects'][pname] += 1
+        else:
+          pattern['projects'][pname] = 1
+  return warning_messages, warning_links, warning_records
+
+
+def write_html(flags, project_names, warn_patterns, html_path, warning_messages,
+               warning_links, warning_records, header_str):
+  """Write warnings html file."""
+  if html_path:
+    with open(html_path, 'w') as f:
+      dump_html(flags, f, warning_messages, warning_links, warning_records,
+                header_str, warn_patterns, project_names)
+
+
+def write_out_csv(flags, warn_patterns, warning_messages, warning_links,
+                  warning_records, header_str, project_names):
+  """Write warnings csv file."""
+  if flags.csvpath:
+    with open(flags.csvpath, 'w') as f:
+      dump_csv(csv.writer(f, lineterminator='\n'), warn_patterns)
+
+  if flags.gencsv:
+    dump_csv(csv.writer(sys.stdout, lineterminator='\n'), warn_patterns)
+  else:
+    dump_html(flags, sys.stdout, warning_messages, warning_links,
+              warning_records, header_str, warn_patterns, project_names)
+
+
+def process_log(logfile, flags, project_names, project_patterns, warn_patterns,
+                html_path, use_google3, create_launch_subprocs_fn,
+                classify_warnings_fn, logfile_object):
+  # pylint: disable=g-doc-args
+  # pylint: disable=g-doc-return-or-yield
+  """Function that handles processing of a log.
+
+  This is isolated into its own function (rather than just taking place in main)
+  so that it can be used by both warn.py and the borg job process_gs_logs.py, to
+  avoid duplication of code.
+  Note that if the arguments to this function change, process_gs_logs.py must
+  be updated accordingly.
+  """
+  if logfile_object is None:
+    with io.open(logfile, encoding='utf-8') as log:
+      warning_lines_and_links, header_str = parse_input_file(log, flags)
+  else:
+    warning_lines_and_links, header_str = parse_input_file(
+        logfile_object, flags)
+  warning_messages, warning_links, warning_records = parallel_classify_warnings(
+      warning_lines_and_links, flags, project_names, project_patterns,
+      warn_patterns, use_google3, create_launch_subprocs_fn,
+      classify_warnings_fn)
+
+  write_html(flags, project_names, warn_patterns, html_path,
+             warning_messages, warning_links, warning_records,
+             header_str)
+
+  return warning_messages, warning_links, warning_records, header_str
+
+
+def common_main(use_google3, create_launch_subprocs_fn, classify_warnings_fn,
+                logfile_object=None):
+  """Shared main function for Google3 and non-Google3 versions of warn.py."""
+  flags = parse_args(use_google3)
+  warn_patterns = get_warn_patterns(flags.platform)
+  project_list = get_project_list(flags.platform)
+
+  project_names = get_project_names(project_list)
+  project_patterns = [re.compile(p[1]) for p in project_list]
+
+  # html_path=None because we output html below if not outputting CSV
+  warning_messages, warning_links, warning_records, header_str = process_log(
+      logfile=flags.log, flags=flags, project_names=project_names,
+      project_patterns=project_patterns, warn_patterns=warn_patterns,
+      html_path=None, use_google3=use_google3,
+      create_launch_subprocs_fn=create_launch_subprocs_fn,
+      classify_warnings_fn=classify_warnings_fn,
+      logfile_object=logfile_object)
+
+  write_out_csv(flags, warn_patterns, warning_messages, warning_links,
+                warning_records, header_str, project_names)
+
+  # Return these values, so that caller can use them, if desired.
+  return flags, warning_messages, warning_records, warn_patterns