Move ProxyResolver to common.

HttpFetcher depends on it and HttpFetcher is in common.

Bug: 28171891
Test: mma
Change-Id: I1783821c4a7d6785ee23df1cde648a3e1ea8fadf
diff --git a/update_engine.gyp b/update_engine.gyp
index c90c018..358f64a 100644
--- a/update_engine.gyp
+++ b/update_engine.gyp
@@ -168,6 +168,7 @@
         'common/multi_range_http_fetcher.cc',
         'common/platform_constants_chromeos.cc',
         'common/prefs.cc',
+        'common/proxy_resolver.cc',
         'common/subprocess.cc',
         'common/terminator.cc',
         'common/utils.cc',
@@ -270,7 +271,6 @@
         'p2p_manager.cc',
         'payload_state.cc',
         'power_manager_chromeos.cc',
-        'proxy_resolver.cc',
         'real_system_state.cc',
         'shill_proxy.cc',
         'update_attempter.cc',
@@ -518,6 +518,7 @@
             'common/hwid_override_unittest.cc',
             'common/mock_http_fetcher.cc',
             'common/prefs_unittest.cc',
+            'common/proxy_resolver_unittest.cc',
             'common/subprocess_unittest.cc',
             'common/terminator_unittest.cc',
             'common/test_utils.cc',
@@ -571,7 +572,6 @@
             'payload_generator/topological_sort_unittest.cc',
             'payload_generator/zip_unittest.cc',
             'payload_state_unittest.cc',
-            'proxy_resolver_unittest.cc',
             'testrunner.cc',
             'update_attempter_unittest.cc',
             'update_boot_flags_action_unittest.cc',