An observer for top level notifications of scene changes. In order to receive more granular change notifications a user may install mir::scene::SurfaceObserver in surface_added
A policy based window manager. This exists to initialize BasicWindowManager and the WMPolicy (in an awkward manner). TODO revisit this initialization sequence
The interface through which the policy instructs the controller. These functions assume that the BasicWindowManager data structures can be accessed freely. I.e. should only be invoked by the policy handle_... methods (where any necessary locks are held)