Android requires additional stats in mallinfo. While we can provide
right away the number of bytes mapped (Primary+Secondary), there was
no way to get the number of free bytes (only makes sense for the
Primary since the Secondary unmaps everything on deallocation).
An approximation could be StatMapped - StatAllocated, but since we
are mapping in 1<<17 increments for the 64-bit Primary, it's fairly
So we introduce StatFree (note it's Free, not Freed!), which
keeps track of the amount of Primary blocks currently unallocated.