[PATCH] [sanitizer] Add a fast version of StackDepotGet() for use in LSan. Add a class that holds a snapshot of the StackDepot optimized for querying by ID. This allows us to speed up LSan dramatically.

[Sergey Matveev]

  > What performance improvement does it provide in your case?

  Leak checking after a run of Chrome unit_tests used to take almost 3 minutes, now takes less than 10 seconds.

http://llvm-reviews.chandlerc.com/D1496

BRANCH
  fix/stackdepot

ARCANIST PROJECT
  compiler-rt