Reviewed by Darin Adler

        https://bugs.webkit.org/show_bug.cgi?id=22046

        Fix a crash when an animation or transition end event handler
        removes the element upon which the transition/animation is running,
        by keeping a reference to the AnimationBase object on the stack.

        Tests: animations/transform-animation-event-destroy-element.html
               transitions/transform-transition-event-destroy-element.html

        * page/animation/AnimationBase.cpp:
        (WebCore::AnimationBase::setChanged):
        (WebCore::AnimationBase::updateStateMachine):
        * page/animation/AnimationBase.h:
        (WebCore::AnimationBase::clearRenderer):
        * page/animation/AnimationController.cpp:
        (WebCore::AnimationControllerPrivate::clear):
        * page/animation/CompositeAnimation.cpp:
        (WebCore::CompositeAnimationPrivate::~CompositeAnimationPrivate):
        * page/animation/CompositeAnimation.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@38768 268f45cc-cd09-0410-ab3c-d52691b4dbfc