Fix a SIGSEGV at background-to-foreground collector transition.

The mem map that's used to create the backup main rosalloc space is
set to PROT_NONE by the compaction and the rosalloc space creation
attempts to write the debug magic number in the first page.

This is a debug build only issue.

Bug: 16854263
Change-Id: I3cc6b7288ee53c006366bb428fb245a909bc3db5
1 file changed