[xhr] Fix global variable leaks (#49)

### screenshot (in https://xhr.spec.whatwg.org/)

![](https://cloud.githubusercontent.com/assets/12539/12636118/555f209c-c5cd-11e5-8464-4d6bf7a9db43.png)
You can view, comment on, or merge this pull request online at:

  https://github.com/whatwg/xhr/pull/49

-- Commit Summary --

  * Fix `window.elms`

-- File Changes --

    M annotate_spec.js (1)

-- Patch Links --

https://github.com/whatwg/xhr/pull/49.patch
https://github.com/whatwg/xhr/pull/49.diff

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/xhr/pull/49