Set / verify stats report timestamps.

Set / verify stats report timestamps.

This CL updates the track report timestamps which were fixed at "0" before
and updates the timestamps in reports for local audio tracks.

Also the timestamps are checked in various tests to make sure no "0" is
returned.

Original CL is at https://webrtc-codereview.appspot.com/51829004/

BUG=webrtc:4316
TBR=hta@webrtc.org, pthatcher@webrtc.org

Committed: https://crrev.com/be24c94c95056e4f0a22039f25f2fa8a27be6b66
Cr-Commit-Position: refs/heads/master@{#9485}

[joachim, 2015-06-22 21:22:32]

The CQ bit was checked by jbauch@webrtc.org

[commit-bot: I haz the power, 2015-06-22 21:22:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1204493002/1

[commit-bot: I haz the power, 2015-06-22 22:06:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-22 22:06:59]

Patchset 1 (id:??) landed as
https://crrev.com/be24c94c95056e4f0a22039f25f2fa8a27be6b66
Cr-Commit-Position: refs/heads/master@{#9485}