Avoid invalidating kInstrumented via suspension

Make sure we no longer trust kInstrumented after executing allocation
code that may suspend.

Don't just switch to the new normal allocator if we were originally
asked for a nonmoving allocation.

Document the convention we need to enforce.

Test: Build and boot AOSP.
Bug: 187958881
Change-Id: Ife722082e87f85e907bfed3f5371865a5642157f
3 files changed