Add je_iterate, je_malloc_disable, and je_malloc_enable

je_iterate calls a callback for every active jemalloc allocation in a
block of memory.  je_malloc_disable prevents allocations to avoid
mutating the jemalloc internal data structures while je_iterate is
running, and je_malloc_enable re-enables allocations.

Bug: 27208635
(cherry picked from commit 6ab5f60a1e0d2b09ec7961b6e2d2c2a39e9c96f2)

Change-Id: Ia5360c940509048532263f3a0dfb296d9e20a8aa
5 files changed