Currently we can set a transform on ServerWindows, but it is not used for targeting calculations.
Also, there's no getters/setters for transform in the client lib (ui::WindowTreeClient, ui::Window), and SetTransform in WmWindowMus in unimplemented.

It might make sense to plug through transform support on the client side first, and update the targeting logic in a subsequent CL - this way it would be easier to make progress on animations (548396).