Revert of Pass the v8::Context through the willDestroyServiceWorkerContextOnWorkerThread event.

Revert of Pass the v8::Context through the willDestroyServiceWorkerContextOnWorkerThread event. (patchset #3 id:60001 of https://codereview.chromium.org/1318643002/ )

Reason for revert:
Canary is frequently crashing, likely due to threading issues with this patch.

Original issue's description:
> Pass the v8::Context through the willDestroyServiceWorkerContextOnWorkerThread event.
>
> Currently it only passes a URL, and this isn't enough to uniquely identify the worker.
> Update extension's dispatcher.cc to use the context.
>
> BUG=501569, 525965
> R=kinuko@chromium.org, thestig@chromium.org
>
> Committed: https://crrev.com/4a0bb926cb1d83fab27b6ad866c04ba481f66268
> Cr-Commit-Position: refs/heads/master@{#346424}

TBR=thestig@chromium.org,kinuko@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=501569, 525965
Committed: https://crrev.com/27acdc49c530aead33a2f8cc273c01cc206822c7
Cr-Commit-Position: refs/heads/master@{#346978}

[not at google - send to devlin, 2015-09-02 18:35:59]

Created Revert of Pass the v8::Context through the
willDestroyServiceWorkerContextOnWorkerThread event.

[commit-bot: I haz the power, 2015-09-02 18:37:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1319603003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1319603003/1

[commit-bot: I haz the power, 2015-09-02 18:39:06]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-02 18:40:26]

Patchset 1 (id:??) landed as
https://crrev.com/27acdc49c530aead33a2f8cc273c01cc206822c7
Cr-Commit-Position: refs/heads/master@{#346978}