[chrome.displaySource] Add a base class for audio and video encoders.

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 1028 matching lines @@
       'renderer/worker_script_context_set.cc',
       'renderer/worker_script_context_set.h',
     ],
     'extensions_renderer_sources_wifi_display': [
       'renderer/api/display_source/wifi_display/wifi_display_elementary_stream_descriptor.cc',
       'renderer/api/display_source/wifi_display/wifi_display_elementary_stream_descriptor.h',
       'renderer/api/display_source/wifi_display/wifi_display_elementary_stream_info.cc',
       'renderer/api/display_source/wifi_display/wifi_display_elementary_stream_info.h',
       'renderer/api/display_source/wifi_display/wifi_display_elementary_stream_packetizer.cc',
       'renderer/api/display_source/wifi_display/wifi_display_elementary_stream_packetizer.h',
+      'renderer/api/display_source/wifi_display/wifi_display_media_encoder.cc',
+      'renderer/api/display_source/wifi_display/wifi_display_media_encoder.h',
       'renderer/api/display_source/wifi_display/wifi_display_media_manager.cc',
       'renderer/api/display_source/wifi_display/wifi_display_media_manager.h',
       'renderer/api/display_source/wifi_display/wifi_display_media_packetizer.cc',
       'renderer/api/display_source/wifi_display/wifi_display_media_packetizer.h',
       'renderer/api/display_source/wifi_display/wifi_display_media_pipeline.cc',
       'renderer/api/display_source/wifi_display/wifi_display_media_pipeline.h',
       'renderer/api/display_source/wifi_display/wifi_display_session.cc',
       'renderer/api/display_source/wifi_display/wifi_display_session.h',
       'renderer/api/display_source/wifi_display/wifi_display_stream_packet_part.h',
       'renderer/api/display_source/wifi_display/wifi_display_transport_stream_packetizer.cc',
@@ skipping 56 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',
     ],
   },
 }