Inline static Create() from renderer/core/animation/css

Identifies and removes usage of static Create() for those classes
defined in //third_party/blink/renderer/core/animation/css.

One note about the Create() method of CSSAnimation and CSSTransition,
it contained the following check:

  DCHECK(timeline && timeline->IsDocumentTimeline());

This is deemed unnecessary and has not been copied inline. The only
uses of these Create() methods were obtaining the Timeline object from
element->GetDocument().Timeline(). This implies that timeline exists
as long as the Document exists (which would trigger a different error)
and it is of type DocumentTimeline, because it was instantiated like
that in the Document constructor:

  https://chromium.googlesource.com/chromium/src/+/5bfed55ceed4a194fd934ab81e47e213dd815fe7/third_party/blink/renderer/core/dom/document.cc#1136

Finally, CompositorKeyframeValueFactory is STATIC_ONLY so its
Create method will not be modified.

Bug: 939691
Change-Id: I9ffcd0688edf7cbab5cc10892254b3384ec2cbd5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1943237
Reviewed-by: Henrique Ferreiro <hferreiro@igalia.com>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Jacobo Aragunde Pérez <jaragunde@igalia.com>
Cr-Commit-Position: refs/heads/master@{#720319}
12 files changed