- Removing null checks as we always have the CodeRange object (it might be
  invalid, but it's there)
- Account for reserved area (Win64) in SetUp so we the caller doesn't need to be
  aware of it

R=ulan@chromium.org

Review-Url: https://codereview.chromium.org/1991253002
Cr-Commit-Position: refs/heads/master@{#36377}