Replace CSSTransitionData::Create(CSSTransition) with clone method.

To copy a CSSTransitionData, we use CSSTransitionData::Create(o).
However, this interface is inconsistent with many other classes that
instead provide a clone method to do the same thing. This patch replaces
the Create method with a Clone method to be consistent.

BUG=628043

Review-Url: https://codereview.chromium.org/2886373002
Cr-Commit-Position: refs/heads/master@{#472720}
2 files changed