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/test/test_util.h b/webrtc/modules/video_coding/test/test_util.h
index 45b88b9..86d3ecf 100644
--- a/webrtc/modules/video_coding/test/test_util.h
+++ b/webrtc/modules/video_coding/test/test_util.h
@@ -29,26 +29,18 @@
  public:
   virtual ~NullEvent() {}
 
-  virtual bool Set() { return true; }
+  bool Set() override { return true; }
 
-  virtual bool Reset() { return true; }
-
-  virtual webrtc::EventTypeWrapper Wait(unsigned long max_time) {  // NOLINT
+  webrtc::EventTypeWrapper Wait(unsigned long max_time) override {  // NOLINT
     return webrtc::kEventTimeout;
   }
-
-  virtual bool StartTimer(bool periodic, unsigned long time) {  // NOLINT
-    return true;
-  }
-
-  virtual bool StopTimer() { return true; }
 };
 
 class NullEventFactory : public webrtc::EventFactory {
  public:
   virtual ~NullEventFactory() {}
 
-  virtual webrtc::EventWrapper* CreateEvent() { return new NullEvent; }
+  webrtc::EventWrapper* CreateEvent() override { return new NullEvent; }
 };
 
 class FileOutputFrameReceiver : public webrtc::VCMReceiveCallback {
@@ -57,7 +49,8 @@
   virtual ~FileOutputFrameReceiver();
 
   // VCMReceiveCallback
-  virtual int32_t FrameToRender(webrtc::VideoFrame& video_frame);  // NOLINT
+  int32_t FrameToRender(webrtc::VideoFrame& video_frame,
+                        rtc::Optional<uint8_t> qp) override;
 
  private:
   std::string out_filename_;