Instead of the longest frame since the last GetStats call, the longest
frame received during last 10 seconds should be returned in GetStats().
Previous way is not a good idea because there are maybe several
consumers of GetStats calls. If not all of them parse timing frame
reports, some of them may be lost.
Also, streamline reporting of TimingFrames via GetStats (remove separate
methods and use VideoReceiveStream::Stats struct instead).
BUG=webrtc:7594
Review-Url: https://codereview.webrtc.org/3008983002
Cr-Commit-Position: refs/heads/master@{#19650}
75204c5ccd