Remove secondary player from Media Sessions

When we switch Android media players, for cast, we no longer want audio
focus changes associated with old player to take effect. To handle this
remove the old player from the Media Sessions.

The new player is responsible for adding itself to the Media Sessions if
it needs to. The remote player doesn't need to, and, after stopping casting
the local player will do so when the user presses play.

BUG=595373

Review URL: https://codereview.chromium.org/1823983002

Cr-Commit-Position: refs/heads/master@{#382613}

content/browser/media/android/browser_media_player_manager.cc

@@ -648,6 +648,9 @@ scoped_ptr<media::MediaPlayerAndroid> BrowserMediaPlayerManager::SwapPlayer(
 #if defined(VIDEO_HOLE)
       ReleaseExternalSurface(player_id);
 #endif
+      MediaWebContentsObserverAndroid::FromWebContents(web_contents_)
+          ->DisconnectMediaSession(render_frame_host_,
+                                   player_id_to_delegate_id_map_[player_id]);
       players_.weak_erase(it);
       players_.push_back(player);
       break;

content/browser/media/android/media_web_contents_observer_android.cc

@@ -95,6 +95,13 @@ bool MediaWebContentsObserverAndroid::RequestPlay(
       has_audio, is_remote, duration);
 }
 
+void MediaWebContentsObserverAndroid::DisconnectMediaSession(
+    RenderFrameHost* render_frame_host,
+    int delegate_id) {
+  session_controllers_manager()->OnEnd(
+      MediaPlayerId(render_frame_host, delegate_id));
+}
+
 #if defined(VIDEO_HOLE)
 void MediaWebContentsObserverAndroid::OnFrameInfoUpdated() {
   for (auto it = media_player_managers_.begin();

content/browser/media/android/media_web_contents_observer_android.h

@@ -57,6 +57,9 @@ class CONTENT_EXPORT MediaWebContentsObserverAndroid
                    bool is_remote,
                    base::TimeDelta duration);
 
+  void DisconnectMediaSession(RenderFrameHost* render_frame_host,
+                              int delegate_id);
+
 #if defined(VIDEO_HOLE)
   void OnFrameInfoUpdated();
 #endif  // defined(VIDEO_HOLE)