binding: Supports static operations/attrs returning non-primitive types.

      Correctly supports static operations/attributes which return non-primitive types, so that the returned object is associated with the caller's context, not associated with |this| which can be faked.

BUG=494640

Review URL: https://codereview.chromium.org/1163893002

git-svn-id: svn://svn.chromium.org/blink/trunk@196373 bbb929c8-8fbe-4397-9dbb-9b2b20218538