- Removes Reserve, Free (overload) and SetProtection methods.
- Updates comment on enum which we still need to distinguish
  between allocated and reserved ArrayBuffers.

Bug: chromium:799573
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I1b4e08f97c22ae6b6af847fbcdde047be62fecf8
Reviewed-on: https://chromium-review.googlesource.com/924603Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Eric Holk <eholk@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51714}