Adds function for computing moving average to visualization tool.

Uses generic functions to plot packet sizes, sequence number delta and bitrate per SSRC. Also detects and prints warnings if delay differences seem unrealistic.

NOTRY=True

Review-Url: https://codereview.webrtc.org/2234883002
Cr-Commit-Position: refs/heads/master@{#13872}
diff --git a/webrtc/tools/event_log_visualizer/analyzer.h b/webrtc/tools/event_log_visualizer/analyzer.h
index d2f569c..6972b37 100644
--- a/webrtc/tools/event_log_visualizer/analyzer.h
+++ b/webrtc/tools/event_log_visualizer/analyzer.h
@@ -29,6 +29,7 @@
   LoggedRtpPacket(uint64_t timestamp, RTPHeader header, size_t total_length)
       : timestamp(timestamp), header(header), total_length(total_length) {}
   uint64_t timestamp;
+  // TODO(terelius): This allocates space for 15 CSRCs even if none are used.
   RTPHeader header;
   size_t total_length;
 };