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This is an effort to only allow using cros orderfiles and thus
hugepages on Chrome OS devices, by checking is_chromeos_device.
Try to eliminate possibly of errors on unsupported platforms like
linux-chromeos.

BUG=chromium:1056198
TEST=linux-chromeos is not using orderfile anymore
TEST=emerge chromeos-chrome still has orderfile with crrev.com/c/1995570

Change-Id: I0b394e6e0731e1236db80c77293c3c44afe19684
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2076404Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Tiancong Wang <tcwang@google.com>
Cr-Commit-Position: refs/heads/master@{#746075}