Re: [web-animations-tests] Upstream animation-effect-timing-easing.html from Blink (#3337)

In rebasing this I also changed the roundtrip tests based on the serialization specified in [CSS Timing](https://drafts.csswg.org/css-timing/#serializing-a-timing-function) (and previously specified in CSS Transitions) as follows:
* step-start and step-end are not canonical forms
* steps(3, end) should serialize to steps(3)

View on GitHub: https://github.com/w3c/web-platform-tests/pull/3337#issuecomment-285589829

Received on Friday, 10 March 2017 06:33:18 UTC