Regression from commit 32a776c8
(Refactor Buttons to use RenderContext when painting, 2015-05-05), the
problem was that we started to call vcl::Window::SetSettings(), which
invokes Invalidate(), which should not happen, since we're in Paint().

Fix this by restoring the old behavior of calling
OutputDevice::SetSettings() directly again.

Change-Id: I57c8e7947764e8cdc2d144be2dd140d3c408255d