Since we have a special guard page at the beginning of the code range on
win64, we need to make sure to adjust the size of the free list
accordingly when creating it.

BUG=chromium:447555
R=hpayer@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/843973002

Cr-Commit-Position: refs/heads/master@{#26012}