Revert 168880 "Make DOMWrapperWorld::current() callable from wor..."

A lot of tests are crashing at DOMWrapperWorld::isIsolatedWorld().
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux/builds/28365

> Make DOMWrapperWorld::current() callable from workers
> 
> This CL does the following two things:
> 
> - Makes DOMWrapperWorld::current() callable from workers. Now that a world is always stored in PerContextDataHolder::world(), DOMWrapperWorld::current() can just look up the PerContextDataHolder::world().
> 
> - Makes DOMWrapperWorld::current() callable even when a window object is being initialized. It's possible that some methods call DOMWrapperWorld::current() while the window is being initialized. To handles the subtle situation, this CL adds DOMWrapperWorld::worldOfInitializingWindow.
> 
> 
> BUG=341032
> NOTRY=true
> 
> Review URL: https://codereview.chromium.org/182903003

TBR=haraken@chromium.org

Review URL: https://codereview.chromium.org/193563003

git-svn-id: svn://svn.chromium.org/blink/trunk@168886 bbb929c8-8fbe-4397-9dbb-9b2b20218538