Add event log visualization of rtp timestamps over time.

BUG=None

Review-Url: https://codereview.webrtc.org/2658073002
Cr-Commit-Position: refs/heads/master@{#16417}
diff --git a/webrtc/tools/event_log_visualizer/analyzer.h b/webrtc/tools/event_log_visualizer/analyzer.h
index 1a82dcc..bb7667f 100644
--- a/webrtc/tools/event_log_visualizer/analyzer.h
+++ b/webrtc/tools/event_log_visualizer/analyzer.h
@@ -85,6 +85,7 @@
   void CreateBweSimulationGraph(Plot* plot);
 
   void CreateNetworkDelayFeedbackGraph(Plot* plot);
+  void CreateTimestampGraph(Plot* plot);
 
   // Returns a vector of capture and arrival timestamps for the video frames
   // of the stream with the most number of frames.