Calculate JitterBufferDelayInMs in the new jitter buffer.

webrtc/modules/video_coding/frame_buffer2.h

Index: webrtc/modules/video_coding/frame_buffer2.h
diff --git a/webrtc/modules/video_coding/frame_buffer2.h b/webrtc/modules/video_coding/frame_buffer2.h
index 7a5326b1fa0ba19a560275aff48ebf19f0b96bec..b41ef2ff340e546517d48c2b12b65649561d9dc3 100644
--- a/webrtc/modules/video_coding/frame_buffer2.h
+++ b/webrtc/modules/video_coding/frame_buffer2.h
@@ -139,6 +139,8 @@ class FrameBuffer {
                                         FrameMap::iterator info)
       EXCLUSIVE_LOCKS_REQUIRED(crit_);
 
+  void UpdateJitterDelay() EXCLUSIVE_LOCKS_REQUIRED(crit_);
+
   void UpdateHistograms() const;
 
   FrameMap frames_ GUARDED_BY(crit_);
@@ -155,10 +157,16 @@ class FrameBuffer {
   int num_frames_buffered_ GUARDED_BY(crit_);
   bool stopped_ GUARDED_BY(crit_);
   VCMVideoProtection protection_mode_ GUARDED_BY(crit_);
-  int num_total_frames_ GUARDED_BY(crit_);
-  int num_key_frames_ 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