- Warn on unused result for OS Allocate, Free, SetPermissions,
  CommitRegion, UncommitRegion functions.
- Adds CHECKS or DCHECK/USE around call sites.

Bug: chromium:756050

Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: Ic00b0a42a1e09bdba013b7fa2b1b4e2b7591bac6
Reviewed-on: https://chromium-review.googlesource.com/769792Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49449}