Move workers' Performance API code to core/timing

Move workers' Performance API code to core/timing

Historically, Performance API for workers was implemented separately
from main thread's. Now, they share a common base class (PerformanceBase),
and workers-specific code is relatively small. So let's merge
modules/performance into core/timing.

BUG=465638
TEST=no functional change; all existing tests should pass

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197303

[Kunihiko Sakamoto, 2015-06-17 07:57:11]

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

[Mike West, 2015-06-17 08:47:19]

On 2015/06/17 at 07:57:12, ksakamoto wrote:
> 

LGTM. I'm fine with moving this into core/, but please wait for kinuko@ to take
a look, as she's closer to worker code than I am.

[kinuko, 2015-06-17 14:10:21]

Slightly wondered if this could be done the other way around (moving timing code
to modules/performance), but looks like there're a few dependencies from other
core code.

ok, lgtm

[Kunihiko Sakamoto, 2015-06-18 01:21:57]

The CQ bit was checked by ksakamoto@chromium.org

[commit-bot: I haz the power, 2015-06-18 01:23:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1186103003/1

[commit-bot: I haz the power, 2015-06-18 01:29:25]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197303