The AlwaysAllocate scope make it impossible to enforce a DCHECK on the maximum
old generation sizes as e.g. large objects can still be allocated using this
scope. Returning false here results in OOM.

R=mstarzinger@chromium.org
BUG=chromium:525448
LOG=N

Review URL: https://codereview.chromium.org/1316183004

Cr-Commit-Position: refs/heads/master@{#30535}