- Sanitize Windows page size / alignment code.
- Reorder some methods to match header file.
- Rename AllocateAlignment to AllocatePageSize to be consistent
  with CommitPageSize.
- Eliminate OS::Allocate overload with is_executable argument.
- Eliminate base::OS::AllocateGuarded - it's not implemented.

Bug: chromium:756050
Change-Id: I046bb019cddde0c0063d617adc2c94a23989d9d1
Reviewed-on: https://chromium-review.googlesource.com/742684
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49114}