Revert 167276 "Remove isolatedWorldForEnteredContext() and isola..."

> Remove isolatedWorldForEnteredContext() and isolatedWorldForIsolate()
> 
> - isolatedWorldForIsolate() is equivalent to DOMWrapperWorld::current()->isIsolatedWorld().
> 
> - isolatedWorldForEnteredContext() is equivalent to DOMWrapperWorld::current()->isIsolatedWorld(). Remember that the world of the current context is equal to the world of the entered context.
> 
> Thus this CL replaces these methods with DOMWrapperWorld::current()->isIsolatedWorld().
> 
> BUG=341032
> R=dcarney@chromium.org, eseidel@chromium.org
> 
> Review URL: https://codereview.chromium.org/137953010

TBR=haraken@chromium.org

Review URL: https://codereview.chromium.org/170893003

git-svn-id: svn://svn.chromium.org/blink/trunk@167360 bbb929c8-8fbe-4397-9dbb-9b2b20218538