Revert of Remove obsolete didClearWindowObject API and bogus FIXME (https://codereview.chromium.org/279153002/)

Reason for revert:
"compile" on "GPU Mac Builder (dbg)" fails.



Original issue's description:
> Remove obsolete didClearWindowObject API and bogus FIXME
> 
> The FIXME was wondering about why the inspector didn't take a certain
> codepath - the reason is that the inspector code only cares about the
> document property being reset, not about the v8 global object being
> created.
> 
> BUG=none
> R=dcarney@chromium.org
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=173864

TBR=dcarney@chromium.org,jochen@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=none

Review URL: https://codereview.chromium.org/276373002

git-svn-id: svn://svn.chromium.org/blink/trunk@173865 bbb929c8-8fbe-4397-9dbb-9b2b20218538