[MediaSession, Android] Adding visibility tests for MediaSession

content/browser/media/session/media_session.cc

Index: content/browser/media/session/media_session.cc
diff --git a/content/browser/media/session/media_session.cc b/content/browser/media/session/media_session.cc
index 0d4ed1e9efaff784cfbc7ae1d3ed3c8a4866265c..e31f53a84868079970b8817431cbaa9026a96195 100644
--- a/content/browser/media/session/media_session.cc
+++ b/content/browser/media/session/media_session.cc
@@ -209,6 +209,12 @@ bool MediaSession::IsControllable() const {
          audio_focus_type_ == Type::Content;
 }
 
+scoped_ptr<base::CallbackList<void(MediaSession::State)>::Subscription>
+MediaSession::RegisterMediaSessionStateChangedCallbackForTest(
+    const StateChangedCallback& cb) {
+  return media_session_state_listeners_.Add(cb);
+}
+
 void MediaSession::SetDelegateForTests(
     scoped_ptr<MediaSessionDelegate> delegate) {
   delegate_ = std::move(delegate);
@@ -317,6 +323,7 @@ void MediaSession::AbandonSystemAudioFocusIfNeeded() {
 }
 
 void MediaSession::UpdateWebContents() {
+  media_session_state_listeners_.Notify(audio_focus_state_);
   static_cast<WebContentsImpl*>(web_contents())->OnMediaSessionStateChanged();
 }