Reviewed by Dirk Schulze.

        REGRESSION (r73369-r73405): transform animation interpolates incorrectly
        https://bugs.webkit.org/show_bug.cgi?id=54793

        After the refactoring in r73380, the ending state for some types of
        accelerated animations was computed incorrectly, because the TransformationMatrix
        wasn't reset to identity before the ending value transformations were applied.

        Fix by cleaning up the code to use explicit, separate values for
        starting and ending values. Only matrix-type animations had this
        issue, but cleaned up other clauses similarly.

        Test: animations/3d/matrix-transform-type-animation.html

        * platform/graphics/ca/GraphicsLayerCA.cpp:
        (WebCore::GraphicsLayerCA::setTransformAnimationEndpoints):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@79168 268f45cc-cd09-0410-ab3c-d52691b4dbfc