Revert of Bind Window focus ability to the ExecutionContext instead of the process.

Revert of Bind Window focus ability to the ExecutionContext instead of the process. (patchset #3 id:40001 of https://codereview.chromium.org/777483004/)

Reason for revert:
Crashing, see bug 441968

Original issue's description:
> Bind Window focus ability to the ExecutionContext instead of the process.
> 
> WindowFocusAllowedIndicator is using a static variable that allows
> the entire process to focus a window. In addition, it is entirely
> stack based which prevents asynchronous methods to use it properly.
> 
> By binding the window focus ability to the ExecutionContext,
> we can allow asynchronous methods but also, reduces the chances
> of unrelated scripts to focus windows when they should not be
> able to. Those two concerns are slightly related because an
> ExecutionContext will now be able to focus a window for a
> long period of time, thus, we do not want other ExecutionContext
> to be able to do that in the meantime.
> 
> This is part of a three-sided CL:
> Part 1: <this>
> Part 2: https://codereview.chromium.org/786403003
> Part 3: https://codereview.chromium.org/722423004
> 
> BUG=440740
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=186849

TBR=jochen@chromium.org,mkwst@chromium.org,mlamouri@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=440740
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=187209

[amineer_google, 2014-12-15 22:57:47]

Created Revert of Bind Window focus ability to the ExecutionContext instead of
the process.

[commit-bot: I haz the power, 2014-12-15 22:58:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/803253003/1

[commit-bot: I haz the power, 2014-12-15 22:58:46]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-12-15 22:58:47]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Ken Rockot(use gerrit already), 2014-12-15 22:59:55]

rockot@chromium.org changed reviewers:
+ rockot@chromium.org

[Ken Rockot(use gerrit already), 2014-12-15 22:59:56]

lgtm pending the revert of https://codereview.chromium.org/786403003 in chromium

[Ken Rockot(use gerrit already), 2014-12-16 02:37:48]

The CQ bit was checked by rockot@chromium.org

[commit-bot: I haz the power, 2014-12-16 02:38:52]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/803253003/1

[commit-bot: I haz the power, 2014-12-16 02:40:27]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=187209