The new animations engine doesn't need to use StyleChangeFromRenderer

The old animation engine needed to use this because the animation was
updated inside RenderObject::setAnimatableStyle, but the new engine
handles animation updates inside Element::styleForRenderer() and the
StyleResolver so we don't need to force a style change if there's
nothing that actually changed.

This patch removes usage of this flag as the first step of getting rid
of this flag entirely. Forcing a new RenderStyle through the styleWillChange
and styleDidChange machinery when nothing actually changed is not something
we should support.

BUG=336552

Review URL: https://codereview.chromium.org/141483009

git-svn-id: svn://svn.chromium.org/blink/trunk@165485 bbb929c8-8fbe-4397-9dbb-9b2b20218538