Revert of Oilpan: Prepare to make ExecutionContext GarbageCollectedMixin.

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

[dcheng, 2014-06-07 08:11:22]

Created Revert of Oilpan: Prepare to make ExecutionContext
GarbageCollectedMixin.

[haraken, 2014-06-07 08:11:49]

LGTM

[commit-bot: I haz the power, 2014-06-07 08:12:06]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dcheng@chromium.org/319333002/1

[commit-bot: I haz the power, 2014-06-07 08:12:37]

Change committed as 175741

[dcheng, 2014-06-07 16:49:13]

A revert of this CL has been created in
https://codereview.chromium.org/319373002/ by dcheng@chromium.org.

The reason for reverting is: This was an incorrect revert--this patch was not
responsible for the crash..