When destroying layer, add children to offscreen layers

If a layer is destroyed, make sure all children are added to the
offscreen layers.  Otherwise, we may dangle a layer that is neither in
current state nor in offscreen layers.
Bug: 141111965
Test: build, boot, manual

Change-Id: Iec6788f10a24cb63faa9b40f246cbde3770d24a7
5 files changed