Add plot of network delay change computed based on transport feedback.

NOTRY=true

Review-Url: https://codereview.webrtc.org/2205803002
Cr-Commit-Position: refs/heads/master@{#13610}
diff --git a/webrtc/tools/event_log_visualizer/analyzer.h b/webrtc/tools/event_log_visualizer/analyzer.h
index bb4db2b..2853e86 100644
--- a/webrtc/tools/event_log_visualizer/analyzer.h
+++ b/webrtc/tools/event_log_visualizer/analyzer.h
@@ -47,6 +47,8 @@
 
   void CreateBweGraph(Plot* plot);
 
+  void CreateNetworkDelayFeebackGraph(Plot* plot);
+
  private:
   class StreamId {
    public: