Pass isolate to v8::Undefined() function

Pass isolate to v8::Undefined() function to avoid implicit call to
v8::Isolate::GetCurrent().

R=haraken
BUG=263412

Review URL: https://chromiumcodereview.appspot.com/24118003

git-svn-id: svn://svn.chromium.org/blink/trunk@157782 bbb929c8-8fbe-4397-9dbb-9b2b20218538