Bug 808146: Declare nsMainThreadPtrHolder as MOZ_FINAL, to fix -Wdelete-non-virtual-dtor build-warning-spam. r=bholley, a=blocking-basecamp+
Bug 828502 - let nsMainThreadPtrHandle::get() handle nullptrs; r=bholley, a=blocking-basecamp+
Bug 827503 - use nsMainThreadPtrHolders when passing XPCWrappedJSes around off main thread, r=bholley,jst a=blocking-basecamp+