Enable H.264 video WebRTC behind run-time flag and add WebRtcBrowserTest for H.264

chrome/chrome_tests.gypi

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'variables': {
     'chrome_browser_extensions_test_support_sources': [
       # A list of sources which is shared between different browser tests.
       'browser/apps/app_browsertest_util.cc',
       'browser/apps/app_browsertest_util.h',
       'browser/extensions/browsertest_util.cc',
@@ skipping 2134 matching lines @@
         '../components/components.gyp:dom_distiller_test_support',
         '../components/components.gyp:guest_view_test_support',
         '../components/components.gyp:history_core_test_support',
         '../components/components.gyp:safe_browsing_db',
         '../components/components.gyp:ssl_config',
         '../components/components.gyp:test_database_manager',
         '../components/components.gyp:translate_core_common',
         '../components/components.gyp:ui_zoom_test_support',
         '../components/components_resources.gyp:components_resources',
         '../components/components_strings.gyp:components_strings',
+        '../content/content.gyp:common_features',
+        '../content/content.gyp:feature_h264_with_openh264_ffmpeg',
         '../content/content_shell_and_tests.gyp:content_browser_test_base',
         '../crypto/crypto.gyp:crypto_test_support',
         '../device/bluetooth/bluetooth.gyp:device_bluetooth_mocks',
         '../device/serial/serial.gyp:device_serial_test_util',
         '../extensions/common/api/api.gyp:extensions_api',
         '../google_apis/google_apis.gyp:google_apis_test_support',
         '../media/cast/cast.gyp:cast_test_utility',
         '../media/media.gyp:media',
         '../net/net.gyp:net',
         '../net/net.gyp:net_test_support',
@@ skipping 1358 matching lines @@
             'browser',
           ],
           'sources': [
             'tools/service_discovery_sniffer/service_discovery_sniffer.cc',
             'tools/service_discovery_sniffer/service_discovery_sniffer.h',
           ],
         }]
     }],
   ],  # 'conditions'
 }