Fix frames dropped statistics

The |frames_dropped| statistics contain not only frames that are dropped
but also frames that are in internal queues. This CL changes that so
that |frames_dropped| only contains frames that are dropped.

Bug: chromium:990317
Change-Id: If222568501b277a75bc514661c4f8f861b56aaed
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/150111
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Johannes Kron <kron@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28968}
diff --git a/modules/video_coding/include/video_coding_defines.h b/modules/video_coding/include/video_coding_defines.h
index 043d8c6..38707ee 100644
--- a/modules/video_coding/include/video_coding_defines.h
+++ b/modules/video_coding/include/video_coding_defines.h
@@ -67,6 +67,8 @@
     return FrameToRender(videoFrame, qp, content_type);
   }
 
+  virtual void OnDroppedFrames(uint32_t frames_dropped);
+
   // Called when the current receive codec changes.
   virtual void OnIncomingPayloadType(int payload_type);
   virtual void OnDecoderImplementationName(const char* implementation_name);
@@ -83,6 +85,8 @@
                                size_t size_bytes,
                                VideoContentType content_type) = 0;
 
+  virtual void OnDroppedFrames(uint32_t frames_dropped) = 0;
+
   virtual void OnFrameBufferTimingsUpdated(int max_decode_ms,
                                            int current_delay_ms,
                                            int target_delay_ms,