Wire up VCMTiming in FrameBuffer2.

The VCMTiming class is now used to set the render time for frames.

BUG=webrtc:5514
R=stefan@webrtc.org

Review URL: https://codereview.webrtc.org/2138873003 .

Cr-Commit-Position: refs/heads/master@{#13621}

webrtc/modules/video_coding/jitter_estimator.h

@@ -50,7 +50,7 @@ class VCMJitterEstimator {
   //          - rttMultiplier  : RTT param multiplier (when applicable).
   //
   // Return value                   : Jitter estimate in milliseconds
-  int GetJitterEstimate(double rttMultiplier);
+  virtual int GetJitterEstimate(double rttMultiplier);
 
   // Updates the nack counter.
   void FrameNacked();