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..6066a66cdd0287f6944eee793516e710cdb862ba 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())
-      << "RendererMediaSessionManager is owned by RenderFrameImpl and is "
-         "destroyed only after all media sessions are destroyed.";
 }
 
 bool RendererMediaSessionManager::OnMessageReceived(const IPC::Message& msg) {
@@ -66,9 +65,14 @@ void RendererMediaSessionManager::Deactivate(
 
 void RendererMediaSessionManager::SetMetadata(
     int session_id, const base::Optional<MediaMetadata>& metadata) {
+  // Non-MainFrames will be ignored.
+  // TODO(zqzhang): print a console warning when metadata from a child frame or
+  // the metadata is dirty. See https://crbug.com/625244.
+  if (!render_frame()->GetWebFrame() ||
+      render_frame()->GetWebFrame()->parent()) {
+    return;
+  }
 
-  // TODO(zqzhang): print a console warning when metadata is dirty. See
-  // https://crbug.com/625244.
   Send(new MediaSessionHostMsg_SetMetadata(
       routing_id(), session_id,
       (!metadata.has_value() ||