Migrate AudioFocusChangeListener to browser and always send GAIN

content/content_browser.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.
 
 {
   'dependencies': [
     '../base/base.gyp:base_static',
     '../crypto/crypto.gyp:crypto',
     '../device/battery/battery.gyp:device_battery',
     '../device/battery/battery.gyp:device_battery_mojo_bindings',
@@ skipping 937 matching lines @@
       'browser/loader/temporary_file_stream.cc',
       'browser/loader/temporary_file_stream.h',
       'browser/loader/throttling_resource_handler.cc',
       'browser/loader/throttling_resource_handler.h',
       'browser/loader/upload_data_stream_builder.cc',
       'browser/loader/upload_data_stream_builder.h',
       'browser/mach_broker_mac.h',
       'browser/mach_broker_mac.mm',
       'browser/manifest/manifest_manager_host.cc',
       'browser/manifest/manifest_manager_host.h',
+      'browser/media/android/audio_focus_manager.cc',
+      'browser/media/android/audio_focus_manager.h',
       'browser/media/android/browser_demuxer_android.cc',
       'browser/media/android/browser_demuxer_android.h',
       'browser/media/android/browser_media_player_manager.cc',
       'browser/media/android/browser_media_player_manager.h',
       'browser/media/android/media_drm_credential_manager.cc',
       'browser/media/android/media_drm_credential_manager.h',
       'browser/media/android/media_resource_getter_impl.cc',
       'browser/media/android/media_resource_getter_impl.h',
       'browser/media/audio_state_provider.cc',
       'browser/media/audio_state_provider.h',
@@ skipping 1068 matching lines @@
         'browser/media/media_web_contents_observer.h',
       ],
     }],
     ['OS == "linux" and use_openssl==1', {
       'dependencies': [
         '../third_party/boringssl/boringssl.gyp:boringssl',
       ],
     }],
   ],
 }