Add missing calls to ScriptWrappable::init in FontFace, LocalCredential and FederatedCredential.

Their absence tripped stronger asserts in multivm's refactoring of ScriptWrappable.

Review URL: https://codereview.chromium.org/469923002

git-svn-id: svn://svn.chromium.org/blink/trunk@180230 bbb929c8-8fbe-4397-9dbb-9b2b20218538