Avoid animation when attributeType="CSS" is used on an animateTransform.

Cherry-pick from https://bugs.webkit.org/show_bug.cgi?id=119748

BUG=292984

Review URL: https://chromiumcodereview.appspot.com/24079006

git-svn-id: svn://svn.chromium.org/blink/trunk@157913 bbb929c8-8fbe-4397-9dbb-9b2b20218538