Reviewed by Dave Hyatt.

        Odd color transitions on anchors with transition-property: all
        https://bugs.webkit.org/show_bug.cgi?id=29911

        When transitioning maybe-invalid colors, if the source and destination
        color are both invalid, then don't animate.

        This fixes an issue where a child element of an element running a color
        transition, with -webkit-transition-property:all, would show a color change.
        This happened because the "maybe invalid color" logic copied the color style
        into -webkit-text-fill-color for both endpoints, causing -webkit-text-fill-color
        to animate while the transition ran, and to then to disappear when the transition
        finished.

        Test: transitions/color-transition-all.html

        * page/animation/AnimationBase.cpp:
        (WebCore::PropertyWrapperMaybeInvalidColor::equals):
        (WebCore::PropertyWrapperMaybeInvalidColor::blend):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@48982 268f45cc-cd09-0410-ab3c-d52691b4dbfc