Revert of Revert of Turn window.postMessage into an ActiveDOMObject (https://codereview.chromium.org/183293002/)

Reason for revert:
This was not the culprit for the LayoutTest crashes

Original issue's description:
> Revert of Turn window.postMessage into an ActiveDOMObject (https://codereview.chromium.org/157243003/)
> 
> Reason for revert:
> A tentative cause for crashes of
> fast/dom/custom/document-register-reentrant-throwing-constructor.html,
> fast/events/before-unload-return-bad-value.html,
> fast/events/onerror-no-constructor.html
> 
> Original issue's description:
> > Turn window.postMessage into an ActiveDOMObject
> > 
> > When JavaScript execution is paused by the debugger messages sent via postMessage should be suspended similar to other events.
> > 
> > BUG=224874
> > 
> > Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168026
> 
> TBR=pfeldman@chromium.org,aandrey@chromium.org,abarth@chromium.org,atwilson@chromium.org,yurys@chromium.org
> NOTREECHECKS=true
> NOTRY=true
> BUG=224874
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=168036

TBR=pfeldman@chromium.org,aandrey@chromium.org,abarth@chromium.org,atwilson@chromium.org,yurys@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=224874

Review URL: https://codereview.chromium.org/183093004

git-svn-id: svn://svn.chromium.org/blink/trunk@168042 bbb929c8-8fbe-4397-9dbb-9b2b20218538