Move audio focus control from media/ to content/ and make it per WebContents.

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 956 matching lines @@
       'browser/manifest/manifest_manager_host.cc',
       'browser/manifest/manifest_manager_host.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/android/media_session.cc',
+      'browser/media/android/media_session.h',
+      'browser/media/android/media_session_observer.h',
       'browser/media/audio_state_provider.cc',
       'browser/media/audio_state_provider.h',
       'browser/media/audio_stream_monitor.cc',
       'browser/media/audio_stream_monitor.h',
       'browser/media/capture/animated_content_sampler.cc',
       'browser/media/capture/animated_content_sampler.h',
       'browser/media/capture/audio_mirroring_manager.cc',
       'browser/media/capture/audio_mirroring_manager.h',
       'browser/media/capture/capture_resolution_chooser.cc',
       'browser/media/capture/capture_resolution_chooser.h',
@@ skipping 1070 matching lines @@
         'browser/media/media_web_contents_observer.h',
       ],
     }],
     ['OS == "linux" and use_openssl==1', {
       'dependencies': [
         '../third_party/boringssl/boringssl.gyp:boringssl',
       ],
     }],
   ],
 }