Re-jigger layers

 Bug: 15185239
 Bug: 15238382

 Make DeferredLayerUpdater ref counted so that
 HardwareLayer:finalizer() works non-crashily on
 leaked layers
 Give DeferredLayerUpdater the ability to have a layer destroyer
 set so that leaked layers can still be recycled on the
 RenderThread
 Order layer updates based off of pushLayerUpdate() calls to fix
 issue with nested layers

Change-Id: I4449cee607f7e5126e02fed7464cf48038e3dfdf