Revert 166402 "V8PerContextDataHolder should know the world asso..."

This is a speculative revert. This CL is depending on a CL that might cause the following crash.
https://code.google.com/p/chromium/issues/detail?id=338122

> V8PerContextDataHolder should know the world associated with the V8PerContextDataHolder
> 
> This is one of incremental steps to clean up code about worlds and contexts.
> 
> - Currently V8PerContextDataHolder understands its associated world only if the world is an isolated world. This CL makes V8PerContextDataHolder understand its associated world always.
> 
> - This CL adds V8PerIsolateData::m_isMainThread and removes V8PerIsolateData::m_workerDOMDataStore.
> 
> BUG=339800
> 
> Review URL: https://codereview.chromium.org/146693019

TBR=haraken@chromium.org

Review URL: https://codereview.chromium.org/155473003

git-svn-id: svn://svn.chromium.org/blink/trunk@166442 bbb929c8-8fbe-4397-9dbb-9b2b20218538