Revert 186849 "Bind Window focus ability to the ExecutionContext..."

Revert 186849 "Bind Window focus ability to the ExecutionContext..."

Reverting this on branch only in an attempt to ship a non-crashy dev.  Still following up on trunk...

BUG=441968
> 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
> 
> Review URL: https://codereview.chromium.org/777483004

TBR=mlamouri@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=187184

[amineer_google, 2014-12-15 22:27:15]

Committed patchset #1 (id:1) manually as r187184.