- Changes assert to reflect that we might exceed the number of attempts
  to allocate a padded memory region while attempting to get an aligned
  allocation and return null instead.

Bug: chromium:813587
Change-Id: I0e225f50b7a64a2f2a72de15322525574445efbd
Reviewed-on: https://chromium-review.googlesource.com/926968Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51401}