Re: selection: Split collapse.html into 2, and extend.html into 3. (#4561)

Notifying @ayg. *([Learn how reviewing works](https://github.com/w3c/web-platform-tests/blob/master/README.md#test-review).)*

View on GitHub: https://github.com/w3c/web-platform-tests/pull/4561#issuecomment-273644099

Received on Thursday, 19 January 2017 00:18:58 UTC