Create thread-safe RendererExtensionRegistry from ExtensionSet

extensions/extensions.gypi

 # Copyright 2015 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': {
     'extensions_common_constants_sources': [
       'common/constants.cc',
       'common/constants.h',
     ],
@@ skipping 912 matching lines @@
       'renderer/native_handler.h',
       'renderer/object_backed_native_handler.cc',
       'renderer/object_backed_native_handler.h',
       'renderer/print_native_handler.cc',
       'renderer/print_native_handler.h',
       'renderer/process_info_native_handler.cc',
       'renderer/process_info_native_handler.h',
       'renderer/programmatic_script_injector.cc',
       'renderer/programmatic_script_injector.h',
       'renderer/render_frame_observer_natives.cc',
+      'renderer/renderer_extension_registry.cc',
+      'renderer/renderer_extension_registry.h',
       'renderer/request_sender.cc',
       'renderer/request_sender.h',
       'renderer/resource_bundle_source_map.cc',
       'renderer/resource_bundle_source_map.h',
       'renderer/resources/app_runtime_custom_bindings.js',
       'renderer/resources/app_window_custom_bindings.js',
       'renderer/resources/binding.js',
       'renderer/resources/context_menus_custom_bindings.js',
       'renderer/resources/declarative_webrequest_custom_bindings.js',
       'renderer/resources/entry_id_manager.js',
@@ skipping 123 matching lines @@
       'test/result_catcher.h',
       'test/test_content_utility_client.cc',
       'test/test_content_utility_client.h',
       'test/test_extensions_client.cc',
       'test/test_extensions_client.h',
       'test/test_permission_message_provider.cc',
       'test/test_permission_message_provider.h',
     ],
   },
 }