Use Blink support to watch CSS selectors directly instead of using a MutationObserver.

chrome/chrome_renderer.gypi

 # Copyright (c) 2012 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.
 
 {
   'targets': [
     {
       'target_name': 'renderer',
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
@@ skipping 169 matching lines @@
         'renderer/playback_extension.h',
         'renderer/resource_bundle_source_map.cc',
         'renderer/resource_bundle_source_map.h',
         'renderer/resources/extensions/app_custom_bindings.js',
         'renderer/resources/extensions/app_window_custom_bindings.js',
         'renderer/resources/extensions/binding.js',
         'renderer/resources/extensions/browser_action_custom_bindings.js',
         'renderer/resources/extensions/chrome_direct_setting.js',
         'renderer/resources/extensions/chrome_setting.js',
         'renderer/resources/extensions/content_setting.js',
-        'renderer/resources/extensions/content_watcher.js',
         'renderer/resources/extensions/context_menus_custom_bindings.js',
         'renderer/resources/extensions/declarative_content_custom_bindings.js',
         'renderer/resources/extensions/declarative_webrequest_custom_bindings.js',
         'renderer/resources/extensions/event.js',
         'renderer/resources/extensions/experimental.offscreenTabs_custom_bindings.js',
         'renderer/resources/extensions/extension_custom_bindings.js',
         'renderer/resources/extensions/feedback_private_custom_bindings.js',
         'renderer/resources/extensions/file_browser_handler_custom_bindings.js',
         'renderer/resources/extensions/file_browser_private_custom_bindings.js',
         'renderer/resources/extensions/file_system_custom_bindings.js',
@@ skipping 249 matching lines @@
               'export_dependent_settings': [
                 '<(allocator_target)',
               ],
             }],
           ],
         }],
       ],
     },
   ],
 }