Add support for DOMTimeStamp and DOMHighResTimeStamp to idlharness.js

Per:
http://www.w3.org/TR/DOM-Level-3-Core/core.html#Core-DOMTimeStamp
and:
http://www.w3.org/TR/hr-time/#sec-DOMHighResTimeStamp

This should work fine. This is annoying me because Gamepad has a DOMHighResTimeStamp propery.