Allow Blink to respond asynchronously to SW Push events (side 3/3)

Allow Blink to respond asynchronously to SW Push events (side 3/3)

This will be necessary once Push events support event.waitUntil to keep the
Service Worker alive until the Promise is resolved
(https://github.com/w3c/push-api/issues/85).

Depends on Blink https://codereview.chromium.org/709103002

BUG=430888, 401438
Committed: https://crrev.com/1763c3912ccad6045d94f29e977e605409edaadd
Cr-Commit-Position: refs/heads/master@{#303454}

[johnme, 2014-11-07 18:44:19]

johnme@chromium.org changed reviewers:
+ michaeln@chromium.org

[michaeln, 2014-11-08 00:18:14]

lgtm

[johnme, 2014-11-09 13:14:46]

The CQ bit was checked by johnme@chromium.org

[commit-bot: I haz the power, 2014-11-09 13:15:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/707243003/1

[commit-bot: I haz the power, 2014-11-09 13:20:29]

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

[commit-bot: I haz the power, 2014-11-09 13:20:30]

Try jobs failed on following builders:
  linux_chromium_gn_dbg on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[johnme, 2014-11-10 11:36:40]

The CQ bit was checked by johnme@chromium.org

[commit-bot: I haz the power, 2014-11-10 11:37:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/707243003/20001

[commit-bot: I haz the power, 2014-11-10 13:19:54]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-11-10 13:20:37]

Patchset 2 (id:??) landed as
https://crrev.com/1763c3912ccad6045d94f29e977e605409edaadd
Cr-Commit-Position: refs/heads/master@{#303454}