Fix memory leakage in VideoSourceHandlerTest.OpenWithoutClose

Fix memory leakage in VideoSourceHandlerTest.OpenWithoutClose

This CL is needed for landing https://codereview.chromium.org/552653005.
https://codereview.chromium.org/552653005 moves MediaStream-related objects
to Oilpan's heap, and the objects are not collected until a next GC is triggered.
Thus some of the Chromium-side tests need to clear those objects and explicitly
trigger a GC in order to make sure that all objects are collected by the end of
each test. Otherwise LSan complains the leakage.

I've already landed a similar fix before: https://codereview.chromium.org/566793002/

I think this CL is a final fix for the memory leakage.

BUG=416466
Committed: https://crrev.com/d9d5b48cddd6e7327a863cdbaac7cc365df4568c
Cr-Commit-Position: refs/heads/master@{#297145}

[haraken, 2014-09-29 01:54:08]

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

[haraken, 2014-09-29 01:54:08]

tommi or perkj: Would you take a look at this change?

I think this is a final fix for landing
https://codereview.chromium.org/552653005.

[perkj_chrome, 2014-09-29 06:23:36]

The CQ bit was checked by perkj@chromium.org

[perkj_chrome, 2014-09-29 06:23:37]

lgtm

lgtm

[commit-bot: I haz the power, 2014-09-29 06:24:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/596923003/1

[commit-bot: I haz the power, 2014-09-29 06:59:56]

Committed patchset #1 (id:1) as c1456aaff5c5241280726f68ff7d5fbb7c64cbae

[commit-bot: I haz the power, 2014-09-29 07:00:28]

Patchset 1 (id:??) landed as
https://crrev.com/d9d5b48cddd6e7327a863cdbaac7cc365df4568c
Cr-Commit-Position: refs/heads/master@{#297145}