Fix valgrind support for dlmalloc space.

Protects redzones at start and end of allocations as no access. Marks
allocations as unknown memory when they are freed. No longer uses
the mempool api since this is not compatible with memory allocators
that use freed memory for internal accounting.

Bug: 7392044
Change-Id: I2501c207c14e2ffc8098ce324ea41cb3b83ccbaf
1 file changed