Correctly keep track of isolates for microtask execution

BUG=487155
R=haraken@chromium.org

Review URL: https://codereview.chromium.org/1161823002

git-svn-id: svn://svn.chromium.org/blink/trunk@195985 bbb929c8-8fbe-4397-9dbb-9b2b20218538
inline PassRefPtrWillBeRawPtr<Event> createScriptLoadEvent()
{
    return Event::create(EventTypeNames::load);
}

inline PassRefPtrWillBeRawPtr<Event> createScriptLoadEvent()
{
    return Event::create(EventTypeNames::load);
}
