Implement MediaMetadata artwork in content

content/browser/media/session/media_session.cc

 // Copyright 2015 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.
 
 #include "content/browser/media/session/media_session.h"
 
 #include "content/browser/media/session/media_session_delegate.h"
 #include "content/browser/media/session/media_session_observer.h"
 #include "content/browser/web_contents/web_contents_impl.h"
 #include "content/public/browser/web_contents.h"
@@ skipping 40 matching lines @@
     session->Initialize();
   }
   return session;
 }
 
 MediaSession::~MediaSession() {
   DCHECK(players_.empty());
   DCHECK(audio_focus_state_ == State::INACTIVE);
 }
 
+void MediaSession::SetMetadata(const MediaMetadata& metadata) {
+  metadata_ = metadata;
+  static_cast<WebContentsImpl*>(web_contents())->OnMediaSessionStateChanged();

[palmer, 2016/06/14 22:06:31]

What guarantees that this cast is safe/correct?

[Zhiqiang Zhang (Slow), 2016/06/20 18:26:49]

WebContentsImpl is the only subclass of WebContents, and MediaSession is valid
as long as WebContents lives, so this cast is safe. Another example is
MediaSession::UpdateWebContents().

+}
+
 bool MediaSession::AddPlayer(MediaSessionObserver* observer,
                              int player_id,
                              Type type) {
   observer->OnSetVolumeMultiplier(player_id, volume_multiplier_);
 
   // If the audio focus is already granted and is of type Content, there is
   // nothing to do. If it is granted of type Transient the requested type is
   // also transient, there is also nothing to do. Otherwise, the session needs
   // to request audio focus again.
   if (audio_focus_state_ == State::ACTIVE &&
@@ skipping 268 matching lines @@
     case State::SUSPENDED:
       uma_helper_.OnSessionSuspended();
       break;
     case State::INACTIVE:
       uma_helper_.OnSessionInactive();
       break;
   }
 }
 
 }  // namespace content