Fix dangling pointer bug when transitioning to background.
Fix dangling pointer bug when transitioning to background.

Dangling pointer left behind from the old rosalloc / dlmalloc
spaces. We now avoid using this pointer by using main_space_
and non_moving_space_ as well as clear the pointer when we remove
the space.

Bug: 16567203

(cherry picked from commit 00b5915828f89daaefd9e8fb215658360f76762c)

Change-Id: I5962929e4a0bb4db6f531d25ee322da7ab3f5dd4

treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst