jemalloc_ptr_info() gives info about any pointer, such as whether it's within a
live or free allocation, and if so, info about that allocation. It's useful for
debugging.
moz_malloc_enclosing_size_of() uses jemalloc_ptr_info() to measure the size of
an allocation from an interior pointer. It's useful for memory reporting,
especially for Rust code.
--HG--
extra : rebase_source : caa19cccf8c2d1f79cf004fe6a408775de5a7b22