We're calling GetCurrentVirtualThread() which is defined in nsThreadUtils.h, so
without including nsThreadUtils.h we'll get a compile error if unified builds
are disabled.
MozReview-Commit-ID: JWCigMqNJDi
This change moves most of the logic for the threadsafety check into
nsAutoOwningThread, rather than having part of the logic live in
nsAutoOwningThread and part of the logic live in nsDebug.h. Changing
this also forces us to clean up a couple of places that replicated the
logic that lived in nsDebug.h as well.
