Add QP sum stats for received streams.

webrtc/video/video_stream_decoder.cc

Index: webrtc/video/video_stream_decoder.cc
diff --git a/webrtc/video/video_stream_decoder.cc b/webrtc/video/video_stream_decoder.cc
index 7a00e42093245f5eb36dd431af9cd94c84a9947e..55a0bfb791669d06afda109eb36e33eb6d6acf6e 100644
--- a/webrtc/video/video_stream_decoder.cc
+++ b/webrtc/video/video_stream_decoder.cc
@@ -75,7 +75,8 @@ VideoStreamDecoder::~VideoStreamDecoder() {
 // callback won't necessarily be called from the decoding thread. The decoding
 // thread may have held the lock when calling VideoDecoder::Decode, Reset, or
 // Release. Acquiring the same lock in the path of decode callback can deadlock.
-int32_t VideoStreamDecoder::FrameToRender(VideoFrame& video_frame) {  // NOLINT
+int32_t VideoStreamDecoder::FrameToRender(VideoFrame& video_frame,
+                                          rtc::Optional<uint8_t> qp) {
   if (pre_render_callback_) {
     // Post processing is not supported if the frame is backed by a texture.
     if (!video_frame.video_frame_buffer()->native_handle()) {
@@ -83,6 +84,7 @@ int32_t VideoStreamDecoder::FrameToRender(VideoFrame& video_frame) {  // NOLINT
     }
   }
 
+  receive_stats_callback_->OnDecodedFrame(qp);

[hbos, 2017/01/26 15:04:45]

Does this really give the same behavior as before?

Could a frame to be decoded and then never rendered (CPU/GPU adaptation)? Or
rendered multiple times (multiple sinks)?
Or maybe that is handled further down.

[sakal, 2017/01/26 15:46:52]

VideoReceiveStream::OnFrame is actually further down than this method. This
method calls IncomingVideoStream::OnFrame which does frame phasing and calls
VideoReceiveStream::OnFrame on another thread.

So calling it here leads to it being called earlier and not being phased but I
don't think that is a problem.

[sprang_webrtc, 2017/01/26 15:48:03]

I think that's all further downstream. incoming_video_stream_ is the first place
I know of that can drop a frame after decoding. 

[hbos, 2017/01/26 15:48:57]

Acknowledged.

   incoming_video_stream_->OnFrame(video_frame);
 
   return 0;