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/video_coding_defines.cc b/modules/video_coding/video_coding_defines.cc
index 0927697..424b23f 100644
--- a/modules/video_coding/video_coding_defines.cc
+++ b/modules/video_coding/video_coding_defines.cc
@@ -12,6 +12,7 @@
 
 namespace webrtc {
 
+void VCMReceiveCallback::OnDroppedFrames(uint32_t frames_dropped) {}
 void VCMReceiveCallback::OnIncomingPayloadType(int payload_type) {}
 void VCMReceiveCallback::OnDecoderImplementationName(
     const char* implementation_name) {}