[Oilpan] Add --js-flags=--expose-gc flag in test

Add --js-flags=--expose-gc flag in OilpanGCTimes test.

It enables renderers without DumpRenderTree to trigger Blink GCs.

BUG=438074, 420515
Committed: https://crrev.com/aa5cd1665963005154d1e8dfa7e757d35f233d10
Cr-Commit-Position: refs/heads/master@{#318888}

[peria, 2015-03-02 05:37:13]

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

[peria, 2015-03-02 05:37:14]

PTL

[kouhei (in TOK), 2015-03-02 05:37:33]

lgtm

[haraken, 2015-03-02 05:39:49]

LGTM

[peria, 2015-03-02 05:41:52]

Sami: could you take a look as an owner?

[peria, 2015-03-03 02:55:16]

peria@chromium.org changed reviewers:
+ skyostil@chromium.org

[peria, 2015-03-03 02:55:16]

I was sorry.
I forgot to add Sami in reviewers.

Sasmi, could you check it?

[Sami, 2015-03-03 12:12:29]

lgtm.

[Hitoshi Yoshida, 2015-03-03 14:38:56]

The CQ bit was checked by peria@google.com

[commit-bot: I haz the power, 2015-03-03 14:39:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/964283002/1

[commit-bot: I haz the power, 2015-03-03 16:34:38]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-03 16:35:34]

Patchset 1 (id:??) landed as
https://crrev.com/aa5cd1665963005154d1e8dfa7e757d35f233d10
Cr-Commit-Position: refs/heads/master@{#318888}