Make {AllocateForCode} return an actual buffer, and move the OOM check
into that method. This allows us to generate more precise OOM messages.

R=mstarzinger@chromium.org

Change-Id: Ie9ed81248fe8068c92eec29a4911ffef43032de2
Reviewed-on: https://chromium-review.googlesource.com/1245769
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56258}