Update WebrtcFrameScheduler to avoid concurrent captures.

remoting/protocol/webrtc_dummy_video_encoder.h

Index: remoting/protocol/webrtc_dummy_video_encoder.h
diff --git a/remoting/protocol/webrtc_dummy_video_encoder.h b/remoting/protocol/webrtc_dummy_video_encoder.h
index 4f59c140ca82a67e27ac6fe94beee11f46acad1e..92b63994ce87c748d02a097adb6c6daccfeab5d5 100644
--- a/remoting/protocol/webrtc_dummy_video_encoder.h
+++ b/remoting/protocol/webrtc_dummy_video_encoder.h
@@ -88,6 +88,10 @@ class WebrtcDummyVideoEncoderFactory
 
   void SetVideoChannelStateObserver(
       base::WeakPtr<VideoChannelStateObserver> video_channel_state_observer);
+  base::WeakPtr<VideoChannelStateObserver>
+  get_video_channel_state_observer_for_tests() {
+    return video_channel_state_observer_;
+  }
 
  private:
   scoped_refptr<base::SingleThreadTaskRunner> main_task_runner_;