Adds remaining missing overrides and nullptr usages, missed due to
an extreme failure in tool usage.
Change-Id: I56abd72975a3999ad13330003c348db40f59aebf
Bug #7146141
This new cache is used in a similar way to LayerCache. It helps
reuse already allocated stencil buffers and thus avoid churning
memory on every frame.
Change-Id: I19551d72da52c40039e65904563600e492c8b193