Keeps it consistent between ASan and LSan.

llvm-svn: 182399

Separate the notions of user-visible chunk and allocator chunk, to facilitate
ASan integration.

llvm-svn: 182256

This is the first in a series of CLs implementing LeakSanitizer.
http://clang.llvm.org/docs/LeakSanitizer.html

llvm-svn: 182245