Show view overlays in hierarchyviewer

ViewOverlays can hold Drawables and Views. But none of these things
show up in hierarchyviewer, so what you see on the screen is not necessarily
what you see in hierarchyviewer.

This CL adds logic to ViewDebug to enable these views/drawables to be displayed.

Issue #8943158 plumb overlay views through into hierarchy viewer

Change-Id: I020e85530a68390b37986269fa3e9e7e43725bab