Clear the FrameBuffer in case of backward jumps in the picture id.

webrtc/modules/video_coding/frame_buffer2.h

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 125 matching lines @@
   // |frame| references.
   // Return false if |frame| will never be decodable, true otherwise.
   bool UpdateFrameInfoWithIncomingFrame(const FrameObject& frame,
                                         FrameMap::iterator info)
       EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   void UpdateJitterDelay() EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
   void UpdateHistograms() const;
 
+  void ClearFramesAndHistory() EXCLUSIVE_LOCKS_REQUIRED(crit_);
+
   FrameMap frames_ GUARDED_BY(crit_);
 
   rtc::CriticalSection crit_;
   Clock* const clock_;
   rtc::Event new_countinuous_frame_event_;
   VCMJitterEstimator* const jitter_estimator_ GUARDED_BY(crit_);
   VCMTiming* const timing_ GUARDED_BY(crit_);
   VCMInterFrameDelay inter_frame_delay_ GUARDED_BY(crit_);
+  uint32_t last_decoded_frame_timestamp_ GUARDED_BY(crit_);
   FrameMap::iterator last_decoded_frame_it_ GUARDED_BY(crit_);
   FrameMap::iterator last_continuous_frame_it_ GUARDED_BY(crit_);
   int num_frames_history_ GUARDED_BY(crit_);
   int num_frames_buffered_ GUARDED_BY(crit_);
   bool stopped_ GUARDED_BY(crit_);
   VCMVideoProtection protection_mode_ GUARDED_BY(crit_);
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(FrameBuffer);
 
   // For WebRTC.Video.JitterBufferDelayInMs metric.
   int64_t accumulated_delay_ = 0;
   int64_t accumulated_delay_samples_ = 0;
 
   // For WebRTC.Video.KeyFramesReceivedInPermille metric.
   int64_t num_total_frames_ = 0;
   int64_t num_key_frames_ = 0;
 };
 
 }  // namespace video_coding
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_FRAME_BUFFER2_H_