Cast: Add JS API to get raw events logs from cast extension.

chrome/renderer/media/cast_session.h

Index: chrome/renderer/media/cast_session.h
diff --git a/chrome/renderer/media/cast_session.h b/chrome/renderer/media/cast_session.h
index 720821fb575054017e9a00fbeed13ba8545b3033..e44cd595cb3887c794871bb0ebc5364d282da496 100644
--- a/chrome/renderer/media/cast_session.h
+++ b/chrome/renderer/media/cast_session.h
@@ -57,8 +57,14 @@ class CastSession : public base::RefCounted<CastSession> {
   void StartUDP(const net::IPEndPoint& local_endpoint,
                 const net::IPEndPoint& remote_endpoint);
 
-  // Get raw event logs and provide the results in |callback| on main thread.
-  void GetEventLogsAndReset(const EventLogsCallback& callback);
+  // Creates an event subscriber for a stream with |stream_id|. The subscriber
+  // will process audio or video events depending on |is_audio|.
+  void StartLogging(const int stream_id, const bool is_audio);
+
+  // Returns raw event logs in serialized format for |stream_id| since
+  // last call and returns result in |callback|.
+  void GetEventLogsAndReset(const EventLogsCallback& callback,
+                            const int stream_id);
 
  private:
   friend class base::RefCounted<CastSession>;