gn2bp: Move response file to `gn_utils`

* This is a GN-specific flag that should live in gn_utils as it might be used in the future when converting to Bazel.

Test: update_results.sh
Change-Id: If870f757cf3ee57a00c571947a7ffea18a7db55d
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index 3737130..faa303e 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -108,7 +108,7 @@
 # Location of the protobuf src dir in the Android source tree.
 android_protobuf_src = 'external/protobuf/src'
 
-response_file = '{{response_file_name}}'
+
 
 # Compiler flags which are passed through to the blueprint.
 cflag_allowlist = [
@@ -737,11 +737,11 @@
     # Handle passing parameters via response file by piping them into the script
     # and reading them from /dev/stdin.
 
-    self.use_response_file = response_file in self.target.args
+    self.use_response_file = gn_utils.RESPONSE_FILE in self.target.args
     if self.use_response_file:
       # Replace {{response_file_contents}} with /dev/stdin
-      self.target.args = ['/dev/stdin' if it == response_file else it for it in
-                          self.target.args]
+      self.target.args = ['/dev/stdin' if it == gn_utils.RESPONSE_FILE else it
+                          for it in self.target.args]
 
   def _sanitize_outputs(self):
     pass
diff --git a/tools/gn2bp/gn_utils.py b/tools/gn2bp/gn_utils.py
index 8f33ca2..0511e8a 100644
--- a/tools/gn2bp/gn_utils.py
+++ b/tools/gn2bp/gn_utils.py
@@ -52,6 +52,8 @@
 ARCH_REGEX = r'(android_x86_64|android_x86|android_arm|android_arm64|host)'
 DEX_REGEX = '.*__dex__%s$' % ARCH_REGEX
 COMPILE_JAVA_REGEX = '.*__compile_java__%s$' % ARCH_REGEX
+RESPONSE_FILE = '{{response_file_name}}'
+
 def repo_root():
   """Returns an absolute path to the repository root."""
   return os.path.join(