Don't reinterpret_cast persistent handles to regular handles.

Like, never, really..

BUG=none
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/631773004

git-svn-id: svn://svn.chromium.org/blink/trunk@183281 bbb929c8-8fbe-4397-9dbb-9b2b20218538