cc: Add some useful layer data to traces.

cc: Add some useful layer data to traces.

These traces were really helpful in tracking out why things were getting
prioritized wrong.

BUG=410625
Committed: https://crrev.com/3895556f535fe8c10a732612cb2c982d8137898c
Cr-Commit-Position: refs/heads/master@{#294728}

[danakj, 2014-09-12 21:17:14]

danakj@chromium.org changed reviewers:
+ vmpstr@chromium.org

[vmpstr, 2014-09-12 22:27:59]

lgtm

[danakj, 2014-09-13 02:02:04]

The CQ bit was checked by danakj@chromium.org

[commit-bot: I haz the power, 2014-09-13 02:04:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/568183002/1

[commit-bot: I haz the power, 2014-09-13 02:57:50]

Committed patchset #1 (id:1) as d1f535f88de47a902d7ce010fbbf181a6bd122a5

[commit-bot: I haz the power, 2014-09-13 03:00:46]

Patchset 1 (id:??) landed as
https://crrev.com/3895556f535fe8c10a732612cb2c982d8137898c
Cr-Commit-Position: refs/heads/master@{#294728}