-Get rid of paintsWithTransform.
-Remove currentTransform. It was only ever called with
IncludeTransformOrigin and on non-null transforms.
-Remove renderableTransform. It was only called on
non-null transforms.
-Remove a layer()->parent() branch. The ASSERT had been
added in a previous patch, but the branch wasn't removed.
-Inline makeMatrixRenderable. It was only called in one
place.
-Add a test to make sure that transform origin is corrrectly
excluded from the transform computedStyle.
R=abarth@chromium.org
Review URL: https://codereview.chromium.org/958463002