Reviewed by Dan Bernstein

        https://bugs.webkit.org/show_bug.cgi?id=25108

        If you remove a class with a transition while that transition is running
        the animation timer will continue to fire after the transition is finished.
        This has no visual indication, but it does drain the processor. And in some
        cases it might even cause a glitch in future animations. Unfortunately there
        is no way to test this without putting in printfs.

        This happens because the animation logic is never traversed after a transition
        is removed, so we never get a chance to cleanup. So I added cleanup in the logic
        that fires the dispatch of the last style change when the animation finishes.

        Test: transitions/remove-transition-style.html

        * page/animation/AnimationController.cpp:
        (WebCore::AnimationControllerPrivate::updateStyleIfNeededDispatcherFired):
        * page/animation/CompositeAnim...