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/2193763002 .
Cr-Commit-Position: refs/heads/master@{#13574}