Oilpan: Force a page navigation GC before starting a V8 GC

Oilpan: Force a page navigation GC before starting a V8 GC

This fixes a performance regression of iframe-append-remove.html.

The fact that the PageNavigation GC is scheduled means that there is
a dead frame. In common cases, a sequence of Oilpan's GC => V8 GC =>
Oilpan's GC is needed to collect the dead frame. So we force the
PageNavigation GC before running the V8 GC.

I don't think this CL affects performance of other benchmarks,
since it would be rare to hit a V8 GC between when a PageNavigation GC
gets scheduled and when the event loop finishes (i.e., when the PageNavigation
GC runs).

BUG=474470
Committed: https://crrev.com/2a1b03ebb89a061babaa85bc88dbecab8081db34
Cr-Commit-Position: refs/heads/master@{#352576}

[haraken, 2015-10-06 08:06:09]

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

[haraken, 2015-10-06 08:06:10]

PTAL

[haraken, 2015-10-06 08:07:01]

On 2015/10/06 08:06:10, haraken wrote:
> PTAL

I think this would be a better fix than
https://codereview.chromium.org/1358813002.

[sof, 2015-10-06 08:35:38]

lgtm

[haraken, 2015-10-06 08:38:04]

The CQ bit was checked by haraken@chromium.org

[commit-bot: I haz the power, 2015-10-06 08:38:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1386453003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1386453003/1

[commit-bot: I haz the power, 2015-10-06 09:57:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-06 09:57:58]

Patchset 1 (id:??) landed as
https://crrev.com/2a1b03ebb89a061babaa85bc88dbecab8081db34
Cr-Commit-Position: refs/heads/master@{#352576}