[Cast] Fix shutdown race between CastReceiverImpl/FrameReceiver and frame emit callback run.

media/cast/receiver/frame_receiver.h

Index: media/cast/receiver/frame_receiver.h
diff --git a/media/cast/receiver/frame_receiver.h b/media/cast/receiver/frame_receiver.h
index 695c8d0a9be9189befa77d4dd1eca4b11cd811d6..67f5417145e3c8d9580059e929c9816dd67a7302 100644
--- a/media/cast/receiver/frame_receiver.h
+++ b/media/cast/receiver/frame_receiver.h
@@ -89,6 +89,13 @@ class FrameReceiver : public RtpPayloadFeedback,
   // EmitAvailableEncodedFrames().
   void EmitAvailableEncodedFramesAfterWaiting();
 
+  // Helper that runs |callback|, passing ownership of |encoded_frame| to it.
+  // This method is used by EmitAvailableEncodedFrames() to return to the event
+  // loop, but make sure that FrameReceiver is still alive before the callback
+  // is run.
+  void EmitOneFrame(const ReceiveEncodedFrameCallback& callback,
+                    scoped_ptr<EncodedFrame> encoded_frame) const;
+
   // Computes the playout time for a frame with the given |rtp_timestamp|.
   // Because lip-sync info is refreshed regularly, calling this method with the
   // same argument may return different results.