[webstorage-tests] Mark Window as a global in webstorage/idlharness.html. (#1589)

This doesn't do anything right now, but will fix some incorrect expectations
once <https://github.com/w3c/testharness.js/pull/104> lands.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/1589

Received on Tuesday, 27 January 2015 11:36:57 UTC