Use UUID for ServiceWorker Client identifier (1/3, blink)

Use UUID for ServiceWorker Client identifier (1/3, blink)

I'm not going to surface the new 'id' field on Client surface yet,
but here're the spec pointers that explains why we do this:
Spec issue: https://github.com/slightlyoff/ServiceWorker/issues/634
More context: https://github.com/slightlyoff/ServiceWorker/issues/609

To be landed in 3 patches:
1/3: THIS
2/3: chromium-side patch https://crrev.com/988063004/
3/3: blink-side cleanup

BUG=464668
TEST=existing tests should pass

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=191591

[kinuko, 2015-03-08 07:03:54]

Patchset #1 (id:1) has been deleted

[kinuko, 2015-03-09 01:57:26]

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

[kinuko, 2015-03-09 01:57:49]

PTL (no changes in API surface yet)

[falken, 2015-03-09 03:39:35]

lgtm

[kinuko, 2015-03-09 08:34:17]

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

[kinuko, 2015-03-09 09:33:07]

Kent-san, could you review Source/web and public/ changes?

[tkent, 2015-03-10 00:20:38]

The CQ bit was checked by tkent@chromium.org

[tkent, 2015-03-10 00:20:38]

lgtm

[tkent, 2015-03-10 00:20:38]

The patchset sent to the CQ was uploaded after l-g-t-m from falken@chromium.org
Link to the patchset: https://codereview.chromium.org/990583002/#ps60001 (title:
" ")

[commit-bot: I haz the power, 2015-03-10 00:21:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/990583002/60001

[commit-bot: I haz the power, 2015-03-10 00:26:23]

Committed patchset #3 (id:60001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=191591