Pass isolate to ScopedPersistent constructor

Pass isolate to ScopedPersistent constructor to avoid implicit call to
v8::Isolate::GetCurrent().

R=haraken
BUG=263412

Review URL: https://chromiumcodereview.appspot.com/23601032

git-svn-id: svn://svn.chromium.org/blink/trunk@157822 bbb929c8-8fbe-4397-9dbb-9b2b20218538