Dispose ApplicationCacheHost on DocumentLoader finalization.

Dispose ApplicationCacheHost on DocumentLoader finalization.

To cater to Oilpan, introduce an explicit dispose() for
ApplicationCacheHost, which the DocumentLoader will call upon when
being finalized.

Without it, a DocumentLoader might clear the Persistent reference to
its ApplicationCacheHost, but it'll still be accessible to embedder
notifications via its WebApplicationCacheHost until the next Oilpan GC
strikes. If so, the callbacks might access a now-dead DocumentLoader.

R=ager
BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=181973

[sof, 2014-09-15 08:39:49]

sigbjornf@opera.com changed reviewers:
+ oilpan-reviews@chromium.org

[sof, 2014-09-15 08:39:50]

Please take a look.

Addressing the http/tests/appcache ASAN failures after
https://codereview.chromium.org/552733003/

Regarding naming, eventually landed on "dispose" rather than "detach". if the
other is preferable, will rename.

[Mads Ager (chromium), 2014-09-15 09:24:01]

ager@chromium.org changed reviewers:
+ ager@chromium.org

[Mads Ager (chromium), 2014-09-15 09:24:01]

LGTM

[sof, 2014-09-15 11:57:30]

The CQ bit was checked by sigbjornf@opera.com

[commit-bot: I haz the power, 2014-09-15 11:58:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/571003002/1

[haraken, 2014-09-15 12:18:51]

LGTM

[commit-bot: I haz the power, 2014-09-15 12:32:20]

Committed patchset #1 (id:1) as 181973