Add BWE plot to event log analyzer.

The plot is constructed by actually running the congestion controller with
the logged rtp headers and rtcp feedback messages to reproduce the same behavior
as in the real call.

R=phoglund@webrtc.org, terelius@webrtc.org

Review URL: https://codereview.webrtc.org/2188033004 .

Cr-Commit-Position: refs/heads/master@{#13558}

webrtc/tools/event_log_visualizer/plot_base.h

@@ -18,7 +18,7 @@
 namespace webrtc {
 namespace plotting {
 
-enum PlotStyle { LINE_GRAPH, BAR_GRAPH };
+enum PlotStyle { LINE_GRAPH, LINE_DOT_GRAPH, BAR_GRAPH };
 
 struct TimeSeriesPoint {
   TimeSeriesPoint(float x, float y) : x(x), y(y) {}