Implement MediaSession (metadata) per frame [NOT READY, HAS DEPENDENCY]

content/renderer/media/android/renderer_media_session_manager.cc

Index: content/renderer/media/android/renderer_media_session_manager.cc
diff --git a/content/renderer/media/android/renderer_media_session_manager.cc b/content/renderer/media/android/renderer_media_session_manager.cc
index 3d53c5d13416d57d3464c3d393d032642b9743f0..4e098d6c0f37f75b8298647a93129ff981d2ee14 100644
--- a/content/renderer/media/android/renderer_media_session_manager.cc
+++ b/content/renderer/media/android/renderer_media_session_manager.cc
@@ -9,8 +9,10 @@
 #include "content/common/media/media_metadata_sanitizer.h"
 #include "content/common/media/media_session_messages_android.h"
 #include "content/public/common/media_metadata.h"
+#include "content/public/renderer/render_frame.h"
 #include "content/public/renderer/render_thread.h"
 #include "content/renderer/media/android/webmediasession_android.h"
+#include "third_party/WebKit/public/web/WebLocalFrame.h"
 
 namespace content {
 
@@ -20,9 +22,6 @@ RendererMediaSessionManager::RendererMediaSessionManager(
       next_session_id_(blink::WebMediaSession::DefaultID + 1) {}
 
 RendererMediaSessionManager::~RendererMediaSessionManager() {
-  DCHECK(sessions_.empty())

[whywhat, 2016/09/13 16:23:26]

why removing this? no longer true?

[Zhiqiang Zhang (Slow), 2016/09/13 17:27:29]

It was even not true before this patch.
blink::MediaSession has a unique_ptr<> pointing at WebMediaSession.
WebMediaSession unregisters itself in the dtor.
Since blink::MediaSession is gc'ed, it is quite likely that
RenderMediaSessionManager is destroyed and WebMediaSession is still alive,
hitting this DCHECK.

To trigger it, just go to the MediaSession test page, play the audio, and
navigate to another URL.

-      << "RendererMediaSessionManager is owned by RenderFrameImpl and is "
-         "destroyed only after all media sessions are destroyed.";
 }
 
 bool RendererMediaSessionManager::OnMessageReceived(const IPC::Message& msg) {
@@ -66,6 +65,9 @@ void RendererMediaSessionManager::Deactivate(
 
 void RendererMediaSessionManager::SetMetadata(
     int session_id, const base::Optional<MediaMetadata>& metadata) {
+  // Non-MainFrames will be ignored.
+  if (render_frame()->GetWebFrame()->parent())
+    return;

[whywhat, 2016/09/13 16:23:26]

print a message here too?
are we 100% sure GetWebFrame() never returns null?

[Zhiqiang Zhang (Slow), 2016/09/13 18:51:52]

Seems not 100%. Fixed.

 
   // TODO(zqzhang): print a console warning when metadata is dirty. See
   // https://crbug.com/625244.