Revert of Revert of Oilpan: Prepare to make ExecutionContext GarbageCollectedMixin.

Revert of Revert of Oilpan: Prepare to make ExecutionContext GarbageCollectedMixin. (https://codereview.chromium.org/319333002/)

Reason for revert:
This was an incorrect revert--this patch was not responsible for the crash.

Original issue's description:
> Revert of Oilpan: Prepare to make ExecutionContext GarbageCollectedMixin. (https://codereview.chromium.org/318023002/)
> 
> Reason for revert:
> plugins/document-open.html is crashing on debug layout bots
> 
> Original issue's description:
> > Oilpan: Prepare to make ExecutionContext GarbageCollectedMixin.
> > 
> > We creates closures with ExecutionContexts in LocalFileSystem. The
> > ExecutionContext needs to be a CrossThreadPersistent data member of
> > closure. This CL adds ParamStorageTraits specialized to garbage-collected
> > classes.
> > 
> > This is a preparation to remove RefCounted from Node.
> > 
> > BUG=357163
> > 
> > Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175734
> 
> TBR=oilpan-reviews@chromium.org,haraken@chromium.org,tkent@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=357163
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175741

TBR=oilpan-reviews@chromium.org,haraken@chromium.org,tkent@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=357163
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175747

[dcheng, 2014-06-07 16:49:14]

Created Revert of Revert of Oilpan: Prepare to make ExecutionContext
GarbageCollectedMixin.

[haraken, 2014-06-07 16:49:57]

LGTM, thanks for the gardening!

[commit-bot: I haz the power, 2014-06-07 16:49:58]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dcheng@chromium.org/319373002/1

[commit-bot: I haz the power, 2014-06-07 16:50:34]

Change committed as 175747