Don't clip when drawing a layer

A layer will, by definition, clip its content already. The extra
clip added by the UI toolkit/renderer is wasteful and in some
situations very expensive. If a layered view is rotated, the clip
will be transformed into a non-rectangular region, thus forcing
the renderer to rely on the stencil buffer. The whole point of
using layers is to draw efficiently so let's avoid this case.

Change-Id: I813465f6468cc386b84a4d058c11a258fef8507a