Ensure JavaScript equality when serviceWorker.register resolves to an existing worker [1/3]

Ensure JavaScript equality when serviceWorker.register resolves to an existing worker [1/3]

If there's an existing registration for the scope and script url,
serviceWorker.register resolves to the active worker for that registration. This
patch modifies the dispatcher to reuse an existing ServiceWorkerHandle, so
service workers that are the same have JavaScript equality.

Three-sided patch:
[1] Blink: ServiceWorker::from can be called from CallbackPromiseAdapter
for a SW that was already registered and reached the proxy "ready" state
[2] Chromium: https://codereview.chromium.org/412833002/
[3] Blink: https://codereview.chromium.org/411863003

BUG=395928
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178810

[falken, 2014-07-23 11:09:14]

PTAL.

Since register is changing, this is not so important, but it  helps for writing
tests for "cancelled"
unregistration:<https://code.google.com/p/chromium/issues/detail?id=388095#c16>

[nhiroki, 2014-07-24 02:08:46]

lgtm

[falken, 2014-07-24 02:17:08]

The CQ bit was checked by falken@chromium.org

[commit-bot: I haz the power, 2014-07-24 02:17:50]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/falken@chromium.org/409403002/1

[commit-bot: I haz the power, 2014-07-24 03:22:35]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/18624)

[commit-bot: I haz the power, 2014-07-24 04:29:52]

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

[commit-bot: I haz the power, 2014-07-24 04:29:53]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/18629)

[falken, 2014-07-24 04:47:06]

The CQ bit was checked by falken@chromium.org

[commit-bot: I haz the power, 2014-07-24 04:47:18]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/falken@chromium.org/409403002/1

[commit-bot: I haz the power, 2014-07-24 05:06:51]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/18640)

[commit-bot: I haz the power, 2014-07-24 05:18:28]

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

[commit-bot: I haz the power, 2014-07-24 05:18:29]

Try jobs failed on following builders:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/18645)

[falken, 2014-07-24 05:25:41]

The CQ bit was checked by falken@chromium.org

[commit-bot: I haz the power, 2014-07-24 05:26:52]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/falken@chromium.org/409403002/1

[commit-bot: I haz the power, 2014-07-24 06:20:28]

Change committed as 178810