Introduce ContentSettingsClient interface

components/content_settings.gypi

 # Copyright 2014 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': [
     {
       # GN version: //components/content_settings/core/browser
       'target_name': 'content_settings_core_browser',
       'type': 'static_library',
       'dependencies': [
         '../base/base.gyp:base',
         'content_settings_core_common',
       ],
       'variables': { 'enable_wexit_time_destructors': 1, },
       'include_dirs': [
         '..',
       ],
       'sources': [
         # Note: sources list duplicated in GN build.
+        'content_settings/core/browser/content_settings_client.h',
         'content_settings/core/browser/content_settings_details.cc',
         'content_settings/core/browser/content_settings_details.h',
         'content_settings/core/browser/content_settings_observer.h',
         'content_settings/core/browser/content_settings_provider.h',
         'content_settings/core/browser/content_settings_observable_provider.cc',
         'content_settings/core/browser/content_settings_observable_provider.h',
         'content_settings/core/browser/content_settings_origin_identifier_value_map.cc',
         'content_settings/core/browser/content_settings_origin_identifier_value_map.h',
         'content_settings/core/browser/content_settings_rule.cc',
         'content_settings/core/browser/content_settings_rule.h',
@@ skipping 21 matching lines @@
         'content_settings/core/common/content_settings_pattern.h',
         'content_settings/core/common/content_settings_pattern_parser.cc',
         'content_settings/core/common/content_settings_pattern_parser.h',
         'content_settings/core/common/content_settings_types.h',
         'content_settings/core/common/permission_request_id.h',
         'content_settings/core/common/permission_request_id.cc',
       ],
     },
   ],
 }