Add ScriptForbiddenScope to weak callbacks of DOM wrappers

It's dangerous to allow arbitrary JavaScript to run during a V8 GC.

BUG=389445

Review URL: https://codereview.chromium.org/368853002

git-svn-id: svn://svn.chromium.org/blink/trunk@177457 bbb929c8-8fbe-4397-9dbb-9b2b20218538