CSSTransitionDiscrete: implement transition-property-type

This is being discussed here:
w3c/csswg-drafts#8857
The name and values of the property are still under discussion.

This patch does not implement the transition shorthand integration, I'm
going to do that next.

Bug: 1453112
Change-Id: I808cf6bc090ca0f99229eb4a9d9c3c28ccf22afc

css/support/interpolation-testcommon.js

@@ -56,7 +56,7 @@
       target.style.setProperty(property, isNeutralKeyframe(from) ? '' : from);
     },
     nonInterpolationExpectations: function(from, to) {
-      return expectFlip(from, to, 0.5);
+      return expectFlip(from, to, -Infinity);
     },
     notAnimatableExpectations: function(from, to, underlying) {
       return expectFlip(from, to, -Infinity);