Add workerStart attribute to ResourceTiming

Add workerStart attribute to ResourceTiming

This patch adds workerStart attribute to PerformanceResourceTiming
behind the experimental feature flag. This attribute allows developers
to measure ServiceWorker startup time within the resource request,
when the request is routed to a ServiceWorker.

To enforce the attribute ordering, redirectStart and fetchStart now fall
back to workerStart (if available) instead of startTime.

spec: https://w3c.github.io/resource-timing/#widl-PerformanceResourceTiming-workerStart

BUG=465640
TEST=http/tests/serviceworker/resource-timing.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196110

[Kunihiko Sakamoto, 2015-05-28 04:10:49]

Patchset #1 (id:1) has been deleted

[Kunihiko Sakamoto, 2015-05-28 06:08:01]

Patchset #1 (id:20001) has been deleted

[Kunihiko Sakamoto, 2015-05-28 06:47:41]

ksakamoto@chromium.org changed reviewers:
+ kinuko@chromium.org

[Kunihiko Sakamoto, 2015-05-28 06:47:42]

Kinuko-san, could you review this?

Note: the test depends on https://codereview.chromium.org/1160883004/

[kinuko, 2015-05-28 07:55:22]

lgtm

[Kunihiko Sakamoto, 2015-05-28 07:59:13]

ksakamoto@chromium.org changed reviewers:
+ tkent@chromium.org

[Kunihiko Sakamoto, 2015-05-28 07:59:13]

+tkent for Source/platform (runtime flag only)

[tkent, 2015-05-28 08:04:10]

lgtm

[Kunihiko Sakamoto, 2015-05-29 00:36:16]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2015-05-29 00:36:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1152673004/40001

[commit-bot: I haz the power, 2015-05-29 02:11:39]

Committed patchset #1 (id:40001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196110