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/main.cc b/webrtc/tools/event_log_visualizer/main.cc
index ce8feea..13a5b8a 100644
--- a/webrtc/tools/event_log_visualizer/main.cc
+++ b/webrtc/tools/event_log_visualizer/main.cc
@@ -59,6 +59,9 @@
             false,
             "Plot packet loss in percent for outgoing packets (as perceived by "
             "the send-side bandwidth estimator).");
+DEFINE_bool(plot_timestamps,
+            false,
+            "Plot the rtp timestamps of all rtp and rtcp packets over time.");
 DEFINE_string(
     force_fieldtrials,
     "",
@@ -180,6 +183,10 @@
     analyzer.CreateNetworkDelayFeedbackGraph(collection->AppendNewPlot());
   }
 
+  if (FLAGS_plot_all || FLAGS_plot_timestamps) {
+    analyzer.CreateTimestampGraph(collection->AppendNewPlot());
+  }
+
   collection->Draw();
 
   return 0;