[ServiceWorkerCache] Keep the ServiceWorkerCache alive when handling cache IPCs

[ServiceWorkerCache] Keep the ServiceWorkerCache alive when handling cache IPCs

With this CL, the ServiceWorkerCacheListener holds a reference to the
caches that it calls async functions on to ensure that the callbacks
are called.

Note: Keeping the cache alive longer does not alter cache deletion
behavior as cache deletion destroys the cache's backend but not the
ServiceWorkerCache object itself.

BUG=429161
Committed: https://crrev.com/ec8c1abe68ef1d68e559b8b4ce2a3ee0e23c490a
Cr-Commit-Position: refs/heads/master@{#302336}

[jkarlin, 2014-10-31 15:12:58]

jkarlin@chromium.org changed reviewers:
+ horo@chromium.org, michaeln@chromium.org

[jkarlin, 2014-10-31 15:12:59]

michaeln@chromium.org: Please review changes in all

horo@chromium.org: Please review changes in all

Thanks!

[michaeln, 2014-10-31 21:16:44]

lgtm

[jkarlin, 2014-10-31 21:28:22]

The CQ bit was checked by jkarlin@chromium.org

[commit-bot: I haz the power, 2014-10-31 21:29:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/682383005/20001

[commit-bot: I haz the power, 2014-10-31 22:14:50]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-10-31 22:15:37]

Patchset 2 (id:??) landed as
https://crrev.com/ec8c1abe68ef1d68e559b8b4ce2a3ee0e23c490a
Cr-Commit-Position: refs/heads/master@{#302336}