Implement Audio Focus Manager for desktop.

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',
     '../cc/cc.gyp:cc',
     '../cc/cc.gyp:cc_surfaces',
     '../components/components.gyp:display_compositor',
@@ skipping 1058 matching lines @@
       'browser/media/media_internals_handler.cc',
       'browser/media/media_internals_handler.h',
       'browser/media/media_internals_proxy.cc',
       'browser/media/media_internals_proxy.h',
       'browser/media/media_internals_ui.cc',
       'browser/media/media_internals_ui.h',
       'browser/media/media_web_contents_observer.cc',
       'browser/media/media_web_contents_observer.h',
       'browser/media/midi_host.cc',
       'browser/media/midi_host.h',
+      'browser/media/session/audio_focus_manager.cc',
+      'browser/media/session/audio_focus_manager.h',
       'browser/media/session/media_session.cc',
       'browser/media/session/media_session.h',
       'browser/media/session/media_session_controller.cc',
       'browser/media/session/media_session_controller.h',
       'browser/media/session/media_session_controllers_manager.cc',
       'browser/media/session/media_session_controllers_manager.h',
       'browser/media/session/media_session_delegate.h',
       'browser/media/session/media_session_delegate_android.cc',
       'browser/media/session/media_session_delegate_android.h',
       'browser/media/session/media_session_delegate_default.cc',
@@ skipping 1063 matching lines @@
       ],
     }],
     ['OS != "mac" and OS != "android"', {
       'sources!': [
         'browser/gpu/gpu_surface_tracker.cc',
         'browser/gpu/gpu_surface_tracker.h',
       ],
     }],
   ],
 }