Reviewed by Dan Bernstein.

        Animation with a timing function property in a keyframe eats CPU
        https://bugs.webkit.org/show_bug.cgi?id=27856
        <rdar://problem/7104476> Animation demo uses lots of CPU

        Don't include animation-timing-function in the list of properties to
        animate in a keyframe animation, because this property is not animated;
        instead, it describes the timing function to apply to this keyframe.

        This prevents the animation code from thinking that there's a property
        that it has to software-animate, and thus firing the animation timer frequently.

        Not testable because there is no visible impact.

        * css/CSSStyleSelector.cpp:
        (WebCore::CSSStyleSelector::keyframeStylesForAnimation): Don't add
        CSSPropertyWebkitAnimationTimingFunction to the list of properties to animate.

        * page/animation/KeyframeAnimation.cpp
        (WebCore::KeyframeAnimation::getKeyframeAnimationInterval): Add a comment

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@46603 268f45cc-cd09-0410-ab3c-d52691b4dbfc