Add QP sum stats for received streams.

webrtc/modules/video_coding/include/video_coding_defines.h

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 45 matching lines @@
 
 struct VCMFrameCount {
   uint32_t numKeyFrames;
   uint32_t numDeltaFrames;
 };
 
 // Callback class used for passing decoded frames which are ready to be
 // 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;
   }
   // Called when the current receive codec changes.
   virtual void OnIncomingPayloadType(int payload_type) {}
   virtual void OnDecoderImplementationName(const char* implementation_name) {}
 
  protected:
   virtual ~VCMReceiveCallback() {}
 };
@@ skipping 89 matching lines @@
  public:
   virtual void RequestKeyFrame() = 0;
 
  protected:
   virtual ~KeyFrameRequestSender() {}
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_INCLUDE_VIDEO_CODING_DEFINES_H_