Clear FrameBuffer if there were no frames received for 10 minutes

This is a workaround for the case when there are no video frames in a
call for a very long time, such that RTP timestamps wraparound and
FrameBuffer can't figure out if the frame is older or newer.

Bug: webrtc:9974
Change-Id: Ie1eaa4938813dbbd637ddcbe7ff118ead2bfa4a9
Reviewed-on: https://webrtc-review.googlesource.com/c/109882
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25548}

modules/video_coding/frame_buffer2.h

@@ -79,6 +79,9 @@ class FrameBuffer {
   // Updates the RTT for jitter buffer estimation.
   void UpdateRtt(int64_t rtt_ms);
 
+  // Clears the FrameBuffer, removing all the buffered frames.
+  void Clear();
+
  private:
   struct FrameInfo {
     FrameInfo();