Add QP sum stats for received streams.

webrtc/modules/video_coding/include/video_coding_defines.h

Index: webrtc/modules/video_coding/include/video_coding_defines.h
diff --git a/webrtc/modules/video_coding/include/video_coding_defines.h b/webrtc/modules/video_coding/include/video_coding_defines.h
index 122ddc6315c5b85a3a5ac5c7cd4654ecb6cc6880..5f472d2b3002703cfbf4ea9ae031eb9b15e14690 100644
--- a/webrtc/modules/video_coding/include/video_coding_defines.h
+++ b/webrtc/modules/video_coding/include/video_coding_defines.h
@@ -63,7 +63,7 @@ struct VCMFrameCount {
 // rendered.
 class VCMReceiveCallback {
  public:
-  virtual int32_t FrameToRender(VideoFrame& videoFrame) = 0;  // NOLINT
+  virtual int32_t FrameToRender(VideoFrame& videoFrame, int qp) = 0;  // NOLINT

[hbos, 2017/01/25 11:31:12]

Can you use rtc::Optional<uint64_t> instead?

[sakal, 2017/01/25 12:39:34]

This is something I thought about. I am not sure if we should use rtc::Optional
as a function argument? For non basic types, it is recommended to use const
pointer instead. rtc::Optional probably has worse performance but I doubt it is
anything noticeable since this is only called once per frame. Any comments?

[sprang_webrtc, 2017/01/25 15:59:14]

Agree that optional would be slightly more readable and that the overhead
shouldn't be terrible.
Imho this whole interface should be moved out of vcm and refactored. 

   virtual int32_t ReceivedDecodedReferenceFrame(const uint64_t pictureId) {
     return -1;
   }