Revert 166309 "Implement DOMWrapperWorlds for workers"

> Implement DOMWrapperWorlds for workers
> 
> Currently we have DOMWrapperWorlds for a main world and isolated worlds
> but don't have DOMWrapperWorlds for worker worlds.
> 
> This design is inconsistent and causes a couple of mess in V8 binding.
> For example, we have to be careful that we're in the main thread when
> calling DOMWrapperWorld::current() (since workers don't have DOMWrapperWorlds).
> 
> We should implement DOMWrapperWorld for worker worlds as well, so that
> we can treat all worlds consistently.
> 
> (Note: This change is necessary for inserting assertions to ScopedPersistent
> to verify that ScopedPersistent doesn't leak between worlds.)
> 
> BUG=339800
> TBR=abarth (for web/)
> 
> Review URL: https://codereview.chromium.org/151443002

TBR=haraken@chromium.org

Review URL: https://codereview.chromium.org/155373004

git-svn-id: svn://svn.chromium.org/blink/trunk@166437 bbb929c8-8fbe-4397-9dbb-9b2b20218538