Change MemMap::maps_ to not be global variable

Runtime.exit() was causing globals to get destructed at the same time
that another thread was using it for allocating a new mem map.

(cherry picked from commit 6e88ef6b604a7a945a466784580c42e6554c1289)

Bug: 17962201
Change-Id: I400cb7b8141d858f3c08a6fe59a02838c04c6962
9 files changed