Support for overlay files that aren't present in base assets.
Support for overlay files that aren't present in base assets.

This is required to include new textures / meshes etc. that we want
in the mod that don't exist in the original asset set.

Bug: 25596948
Change-Id: I1760cf72484f7822b421a27b5113f76befce706a

google/zooshi,google/zooshi,google/zooshi,google/zooshi,google/zooshi