Avoid calling v8::Isolate::GetCurrent() twice in V8HiddenPropertyName

Avoid calling v8::Isolate::GetCurrent() twice in V8HiddenPropertyName
by passing the isolate to V8HiddenPropertyName::createString().

R=haraken
BUG=263412

Review URL: https://chromiumcodereview.appspot.com/24218002

git-svn-id: svn://svn.chromium.org/blink/trunk@158011 bbb929c8-8fbe-4397-9dbb-9b2b20218538