Add a leak sanitizer suppression for ResourceFetcher

Add a leak sanitizer suppression for blink::ResourceFetcher::garbageCollectDocumentResources

In content_browsertests, LSAN reports the leak happens in
ResourceFetcher, but its (persistent|ref) pointer is held
by a live instance of Document or DocumentLoader at the
end of the tests.

BUG=506433
Committed: https://crrev.com/2af3041652d3a473995babb42e0d71778427dfdf
Cr-Commit-Position: refs/heads/master@{#337371}

[peria, 2015-07-06 07:57:13]

peria@chromium.org changed reviewers:
+ haraken@chromium.org, oilpan-reviews@chromium.org

[peria, 2015-07-06 07:57:14]

Investigating of http://crrev.com/1124153003/, we think
the leak is not caused by the CL.
https://codereview.chromium.org/1124153003/#msg35

It seems so difficult to confirm and fix the root cause of
this leak that I would like to suppress it now and will fix
it in the future.

[haraken, 2015-07-06 07:58:09]

LGTM

[peria, 2015-07-06 07:58:45]

The CQ bit was checked by peria@chromium.org

[commit-bot: I haz the power, 2015-07-06 07:59:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1216963014/1

[commit-bot: I haz the power, 2015-07-06 08:33:33]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-06 08:34:40]

Patchset 1 (id:??) landed as
https://crrev.com/2af3041652d3a473995babb42e0d71778427dfdf
Cr-Commit-Position: refs/heads/master@{#337371}