Included in this change:
- Change the tag when a pointer is freed so it's easy to detect if
an already freed pointer is being used.
- Move the free backtrace out of the header. This backtrace is only
used under only some circumstances, so no need to allocate space
in all headers for it.
- Add new option free_track_backtrace_num_frames to specify how many
frames to record when the free occurs. This removes the dependency
on the backtrace option to get backtraces.
Bug: 26739265
Change-Id: I76f5209507dcf46af67ada162a7cb2bf282116f2
7993b80f89