Add QP sum stats for received streams.

webrtc/video_decoder.h

Index: webrtc/video_decoder.h
diff --git a/webrtc/video_decoder.h b/webrtc/video_decoder.h
index b8d2c96b1be8da1cb27138f0550302ebe7b378c1..72aec31693b6ef861590ddefb33ccfabd577eaf3 100644
--- a/webrtc/video_decoder.h
+++ b/webrtc/video_decoder.h
@@ -40,6 +40,10 @@ class DecodedImageCallback {
     // The default implementation ignores custom decode time value.
     return Decoded(decodedImage);
   }
+  virtual int32_t DecodedWithQp(VideoFrame& decodedImage, int qp) = 0;
+  virtual int32_t DecodedWithQp(VideoFrame& decodedImage,
+                                int64_t decode_time_ms,
+                                int qp) = 0;

[hbos, 2017/01/25 11:31:13]

I think there should just be one Decoded function with rtc::Optional<uint64_t>
qp. Is decode_time_ms also optional? (If it is but changing to optional is a
pain it can remain int64_t.)

You can add:
virtual int32_t Decoded(VideoFrame& decoded_image,
                        rtc::Optional<int64_t> decode_time_ms,
                        rtc::Optional<uint64_t> qp) {
  Decoded(decoded_image, decode_time_ms ? *decode_time_ms : -1);
}

And a TODO to remove default implementations / other Decoded versions when
upstream projects have implemented it.

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

I removed the other DecodedWithQp method and renamed the other to Decoded. See
other comment for rtc::Optional discussion.

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