The generated FastAccessorAssembler uses IntPtr Load Op to load
from &flags. Therefore, flags should be a pointer type. This fixes
big endian issue.

R=peterssen@google.com, vogelheim@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2266403004
Cr-Commit-Position: refs/heads/master@{#38873}