- Creates a memory management API in v8::internal, which corresponds
  to the existing one in base::OS.
- Implements the new API in terms of the old one.
- Changes all usage of the base::OS API to the one in v8::internal. This
  includes all tests, except platform and OS tests.
- Makes OS:: methods private.
- Moves all LSAN calls into the v8::internal functions.

Bug: chromium:756050
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: Iaa3f022e3e12fdebf937f3c76b6c6455014beb8a
Reviewed-on: https://chromium-review.googlesource.com/794856
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Eric Holk <eholk@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50139}