Chained timing functions are no longer used to implement CSS keyframe animations.

The class ChainedTimingFunction was originally introduced for Web Animations, but can now be retired. 
https://etherpad.mozilla.org/ep/pad/view/ro.Ioh-B8wtvTy/latest 
https://etherpad.mozilla.org/ep/pad/view/ro.0-mAgddgQoP/latest 

BUG=346590

Review URL: https://codereview.chromium.org/177003010

git-svn-id: svn://svn.chromium.org/blink/trunk@169119 bbb929c8-8fbe-4397-9dbb-9b2b20218538