Don't give uid-based categories to app_zygote and isolated processes.

The mapping of UIDs to categories can only take 16 bits, yet isolated
processes start at UID 90000. Additionally, the main purpose of these
categories was to isolate app-private storage, but since isolated
processes don't have access to app-private storage anyway, removing them
doesn't hurt.

The upside is that this allows us to remove mIstrustedsubject from the
app_zygote domain, which prevents app code running in that context from
assigning itself arbitrary categories.

Bug: 157598026
Test: inspect categories of app_zygote and children; verify Chrome works
Merged-In: Idfa8625d939cf30f3683436949bb4f335851622a
Merged-In: I608a096cecffc1c1ff837611ca500a8da3cf1320
Change-Id: I608a096cecffc1c1ff837611ca500a8da3cf1320
4 files changed