Reland: Enable ServiceWorkerPerformanceTimeline flag for stable

Reland: Enable ServiceWorkerPerformanceTimeline flag for stable

This ships User Timing and Resource Timing in Workers, and workerStart
attribute of Resource Timing.

This is a reland of r197722, which is reverted in r199493 to avoid
shipping prefixed Resource Timing APIs. That has been addressed in
r200301; now only unprefixed version of the APIs are available in worker
contexts.

Intent to Implement and Ship:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/htsW078UcFA

BUG=465640, 465641, 465643
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200524

[Kunihiko Sakamoto, 2015-08-13 08:57:33]

ksakamoto@chromium.org changed reviewers:
+ philipj@opera.com, tkent@chromium.org

[philipj_slow, 2015-08-13 11:17:01]

lgtm

[Kunihiko Sakamoto, 2015-08-14 02:22:11]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2015-08-14 02:22:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1289803002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1289803002/1

[commit-bot: I haz the power, 2015-08-14 04:47:18]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-14 04:47:19]

Try jobs failed on following builders:
  win_chromium_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[Kunihiko Sakamoto, 2015-08-14 05:57:19]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2015-08-14 05:57:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1289803002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1289803002/1

[commit-bot: I haz the power, 2015-08-14 07:04:14]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200524