In Web Animations specification, if the animation effect is in none of the any phase, it define as 'Idle' phase. [1]
But, in the gecko, it defined as 'Null' phase.
So we will need to use 'Idle' phase for consistency.
[1] https://w3c.github.io/web-animations/#idle-phase
MozReview-Commit-ID: FlPpYOqdM4X
--HG--
extra : rebase_source : ec294c84f9c77a42d6128e3d43380b80fc130513
Before we begin re-arranging KeyframeEffect.h we move ComputedTiming aside
since putting it in a separate file should make navigating the source
easier.
MozReview-Commit-ID: L5GTFAo00sh
--HG--
extra : rebase_source : e88b6ea092c459afa90831de8469697454e00c5a
Mantaroh Yoshinaga
Daisuke Akatsuka
Brian Birtles