Reland of Add QP sum stats for received streams. (patchset #2 id:300001 of https://codereview.webrtc.org/2680893002/ )

Reason for revert:
Fix the problem.

Original issue's description:
> Revert of Add QP sum stats for received streams. (patchset #10 id:180001 of https://codereview.webrtc.org/2649133005/ )
>
> Reason for revert:
> Breaks downstream build.
>
> Original issue's description:
> > Add QP sum stats for received streams.
> >
> > This is not implemented yet in any of the decoders.
> >
> > BUG=webrtc:6541
> >
> > Review-Url: https://codereview.webrtc.org/2649133005
> > Cr-Commit-Position: refs/heads/master@{#16475}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/ff0e72fd165facac27f0313aa178648782e63bc4
>
> TBR=hta@webrtc.org,hbos@webrtc.org,sprang@webrtc.org,magjed@webrtc.org,stefan@webrtc.org,sakal@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:6541
>
> Review-Url: https://codereview.webrtc.org/2680893002 .
> Cr-Commit-Position: refs/heads/master@{#16480}
> Committed: https://chromium.googlesource.com/external/webrtc/+/69fb2cca4d54f3df7ceddcd1c3e9b0ad80fa849b

TBR=hta@webrtc.org,hbos@webrtc.org,sprang@webrtc.org,magjed@webrtc.org,stefan@webrtc.org,skvlad@webrtc.org
BUG=webrtc:6541

Review-Url: https://codereview.webrtc.org/2681663005
Cr-Commit-Position: refs/heads/master@{#16511}
diff --git a/webrtc/modules/video_coding/generic_decoder.cc b/webrtc/modules/video_coding/generic_decoder.cc
index b1059e8..34500c6 100644
--- a/webrtc/modules/video_coding/generic_decoder.cc
+++ b/webrtc/modules/video_coding/generic_decoder.cc
@@ -48,6 +48,16 @@
 
 int32_t VCMDecodedFrameCallback::Decoded(VideoFrame& decodedImage,
                                          int64_t decode_time_ms) {
+  Decoded(decodedImage,
+          decode_time_ms >= 0 ? rtc::Optional<int32_t>(decode_time_ms)
+                              : rtc::Optional<int32_t>(),
+          rtc::Optional<uint8_t>());
+  return WEBRTC_VIDEO_CODEC_OK;
+}
+
+void VCMDecodedFrameCallback::Decoded(VideoFrame& decodedImage,
+                                      rtc::Optional<int32_t> decode_time_ms,
+                                      rtc::Optional<uint8_t> qp) {
   TRACE_EVENT_INSTANT1("webrtc", "VCMDecodedFrameCallback::Decoded",
                        "timestamp", decodedImage.timestamp());
   // TODO(holmer): We should improve this so that we can handle multiple
@@ -63,15 +73,15 @@
   if (frameInfo == NULL) {
     LOG(LS_WARNING) << "Too many frames backed up in the decoder, dropping "
                        "this one.";
-    return WEBRTC_VIDEO_CODEC_OK;
+    return;
   }
 
   const int64_t now_ms = _clock->TimeInMilliseconds();
-  if (decode_time_ms < 0) {
+  if (!decode_time_ms) {
     decode_time_ms =
-        static_cast<int32_t>(now_ms - frameInfo->decodeStartTimeMs);
+        rtc::Optional<int32_t>(now_ms - frameInfo->decodeStartTimeMs);
   }
-  _timing->StopDecodeTimer(decodedImage.timestamp(), decode_time_ms, now_ms,
+  _timing->StopDecodeTimer(decodedImage.timestamp(), *decode_time_ms, now_ms,
                            frameInfo->renderTimeMs);
 
   decodedImage.set_timestamp_us(
@@ -80,11 +90,10 @@
   // TODO(sakal): Investigate why callback is NULL sometimes and replace if
   // statement with a DCHECK.
   if (callback) {
-    callback->FrameToRender(decodedImage);
+    callback->FrameToRender(decodedImage, qp);
   } else {
     LOG(LS_WARNING) << "No callback, dropping frame.";
   }
-  return WEBRTC_VIDEO_CODEC_OK;
 }
 
 int32_t VCMDecodedFrameCallback::ReceivedDecodedReferenceFrame(