[Web Animations] Accelerated animations don't respect a positive delay value

Animations specified with a positive delay in its Timing options do not visually start animating. It seems undefined, zero, and negative delays are all working as intended.

Example:
https://codepen.io/danwilson/pen/vrjPGx/?editors=0010

In the example, the second row circles are the only ones with positive delays specified and should be animating as well.

Steps to Reproduce:
1. Setup an animation such as:

element.animate([ { transform: 'scale(1)' }, { transform: 'scale(.5)' } ], {
  duration: 1000,
  delay: 500
});


Expected Results:
After 500ms, the element will start to scale to .5 over the course of 1000ms

Actual Results:
No animation occurs, and the element stays at scale(1).

Build: Release 59 (Safari 12.0, WebKit 13606.1.21)

[Radar WebKit Bug Importer]

<rdar://problem/41393393>

[Antoine Quint]

This is specific to accelerated animations.

[Antoine Quint]

Created attachment 345841 [details]
Patch

[Antoine Quint]

Committed r234279: <https://trac.webkit.org/changeset/234279>