DCHECK fix: don't call a given callback twice in ServiceWorkerContextCore

DCHECK fix: don't call a given callback twice in ServiceWorkerContextCore

Another DCHECK fix.
Very simple error, without this 'return' we call the callback twice
which hits assertion in the receiver side in the renderer.

BUG=359438
TEST=manually tested with non-existent service-worker URL in debug build

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=261446

[kinuko, 2014-04-03 07:31:40]

Yet another simple DCHECK error... can you take a look? (sorry for no tests)

[falken, 2014-04-03 07:34:01]

lgtm

[kinuko, 2014-04-03 07:36:06]

The CQ bit was checked by kinuko@chromium.org

[commit-bot: I haz the power, 2014-04-03 07:37:58]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/kinuko@chromium.org/223383003/1

[commit-bot: I haz the power, 2014-04-03 12:19:25]

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

[commit-bot: I haz the power, 2014-04-03 12:19:26]

Commit queue rejected this change because the description was changed
between the time the change entered the commit queue and the time it
was ready to commit. You can safely check the commit box again.

[kinuko, 2014-04-03 15:34:45]

The CQ bit was checked by kinuko@chromium.org

[commit-bot: I haz the power, 2014-04-03 15:35:00]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/kinuko@chromium.org/223383003/1

[commit-bot: I haz the power, 2014-04-03 16:44:21]

Change committed as 261446