bindings/oilpan: Stops using ScriptWrappable pointers already collected by GC.

bindings/oilpan: Stops using ScriptWrappable pointers already collected by GC.

Garbage collected objects can be collected by Oilpan by the time when
ScriptWrappable::secondWeakCallback is called.  In that case,
secondWeakCallback tries to cast a pointer to the already-collected
object to ScriptWrappable*.  CFI(Control Flow Integrity) detects this
cast as a bad cast because vtbl doesn't match.

This CL fixes the issue making it not call secondWeakCallback for
garbage collected objects.

BUG=528798
Committed: https://crrev.com/a923a78d56bf56317f018ed6fbdc42e0ec8fc9a3
git-svn-id: svn://svn.chromium.org/blink/trunk@202133 bbb929c8-8fbe-4397-9dbb-9b2b20218538

[Yuki, 2015-09-11 12:45:29]

yukishiino@chromium.org changed reviewers:
+ haraken@chromium.org

[Yuki, 2015-09-11 12:45:30]

Could you review this CL?

[haraken, 2015-09-11 12:55:54]

Thanks for catching this! LGTM.

[Yuki, 2015-09-11 12:57:46]

The CQ bit was checked by yukishiino@chromium.org

[commit-bot: I haz the power, 2015-09-11 12:58:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1340513002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1340513002/1

[commit-bot: I haz the power, 2015-09-11 13:02:22]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=202133

[commit-bot: I haz the power, 2015-09-23 12:21:46]

Patchset 1 (id:??) landed as
https://crrev.com/a923a78d56bf56317f018ed6fbdc42e0ec8fc9a3