Reland of Fix the video buffer size should take rtt into consideration

modules/video_coding/frame_buffer2.h

Index: modules/video_coding/frame_buffer2.h
diff --git a/modules/video_coding/frame_buffer2.h b/modules/video_coding/frame_buffer2.h
index 32eba8a3cb406fe00985752317eee09d2b3643c6..e502666a81b4010b45290553d79c770dfce531f6 100644
--- a/modules/video_coding/frame_buffer2.h
+++ b/modules/video_coding/frame_buffer2.h
@@ -74,6 +74,9 @@ class FrameBuffer {
   // return immediately.
   void Stop();
 
+  // Updates the RTT for jitter buffer estimation.
+  void UpdateRtt(int64_t rtt_ms);
+
  private:
   struct FrameKey {
     FrameKey() : picture_id(-1), spatial_layer(0) {}