Migrate AudioFocusChangeListener to browser and always send GAIN

content/browser/media/android/browser_media_player_manager.cc

Index: content/browser/media/android/browser_media_player_manager.cc
diff --git a/content/browser/media/android/browser_media_player_manager.cc b/content/browser/media/android/browser_media_player_manager.cc
index 20fd34e89de28e72e243f44ec986366dcabc57af..694f6249b0a6a8542280f082dd51ac1b892c0a8e 100644
--- a/content/browser/media/android/browser_media_player_manager.cc
+++ b/content/browser/media/android/browser_media_player_manager.cc
@@ -136,6 +136,8 @@ BrowserMediaPlayerManager::BrowserMediaPlayerManager(
       fullscreen_player_is_released_(false),
       web_contents_(WebContents::FromRenderFrameHost(render_frame_host)),
       weak_ptr_factory_(this) {
+  audio_focus_manager_.reset(new AudioFocusManager(
+      base::MessageLoopProxy::current(), weak_ptr_factory_.GetWeakPtr()));
 }
 
 BrowserMediaPlayerManager::~BrowserMediaPlayerManager() {
@@ -239,6 +241,7 @@ void BrowserMediaPlayerManager::ReleaseAllMediaPlayers() {
       it != players_.end(); ++it) {
     if ((*it)->player_id() == fullscreen_player_id_)
       fullscreen_player_is_released_ = true;
+    audio_focus_manager_->AbandonAudioFocus((*it)->player_id());
     (*it)->Release();
   }
 }
@@ -253,6 +256,7 @@ void BrowserMediaPlayerManager::OnError(int player_id, int error) {
   Send(new MediaPlayerMsg_MediaError(RoutingID(), player_id, error));
   if (fullscreen_player_id_ == player_id)
     video_view_->OnMediaPlayerError(error);
+  audio_focus_manager_->AbandonAudioFocus(player_id);
 }
 
 void BrowserMediaPlayerManager::OnVideoSizeChanged(
@@ -465,6 +469,7 @@ void BrowserMediaPlayerManager::OnStart(int player_id) {
   if (!player)
     return;
   player->Start();
+  audio_focus_manager_->RequestAudioFocus(player_id);
   if (fullscreen_player_id_ == player_id && fullscreen_player_is_released_) {
     video_view_->OpenVideo();
     fullscreen_player_is_released_ = false;
@@ -599,6 +604,7 @@ void BrowserMediaPlayerManager::ReleaseMediaResources(int player_id) {
   if (external_video_surface_container_)
     external_video_surface_container_->ReleaseExternalVideoSurface(player_id);
 #endif  // defined(VIDEO_HOLE)
+  audio_focus_manager_->AbandonAudioFocus(player_id);
 }
 
 void BrowserMediaPlayerManager::ReleasePlayer(MediaPlayerAndroid* player) {