Revert 170811 "Remove V8PerIsolateData::current()"

This CL broke mac builds.

> Remove V8PerIsolateData::current()
> 
> V8PerIsolateData::current() is not good because it calls v8::Isolate::GetCurrent(). This CL passes Isolate* around and remove V8PerIsolateData::current().
> 
> BUG=357144
> NOTRY=true
> 
> Review URL: https://codereview.chromium.org/222003004

TBR=haraken@chromium.org

Review URL: https://codereview.chromium.org/225153002

git-svn-id: svn://svn.chromium.org/blink/trunk@170816 bbb929c8-8fbe-4397-9dbb-9b2b20218538