Web Animations: Move active animation state to RenderStyle

Decisions about layer creation, composited mappings and whether to apply certain
updates to composited layers depend on the state of active animations. Usually
these states were updated alongside the RenderStyle (as animations are generated
and cancelled by changes to CSS). However there exist some cases where the state
and corresponding layer and compositor information can get out of sync:

1. When starting a transition, an animation with a delay, or certain cases of
   step-function animation is is possible that the RenderStyle is not actually
   changed or compares the same as the previous style.
2. Through the Web Animations API it is possible to start a new animation (for
   example with a start delay) that does not trigger any style recalc before
   starting.

This change moves the necessary parts of the active animation state to
RenderStyle and requests a style recalc when an animation is attached to or
detached from a player.

BUG=360279

Review URL: https://codereview.chromium.org/227333002

git-svn-id: svn://svn.chromium.org/blink/trunk@171005 bbb929c8-8fbe-4397-9dbb-9b2b20218538