Ting-Wei found the issue, I helped uploaded patch to https://chromium-review.googlesource.com/c/586068/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/board-overlays/+/c7643491ecaef37e0b9ae24ac34039898dee6b39

commit c7643491ecaef37e0b9ae24ac34039898dee6b39
Author: Hsin-Yu Chao <hychao@chromium.org>
Date: Thu Jul 27 05:41:55 2017

sand: Fix missing bracket in ebuild

BUG= chromium:748989 
TEST=None

Change-Id: I57a42a814e5e96cbd99448ef95a39dec8ab0714a
Reviewed-on: https://chromium-review.googlesource.com/586068
Commit-Ready: Hsinyu Chao <hychao@chromium.org>
Tested-by: Hsinyu Chao <hychao@chromium.org>
Reviewed-by: Ting-Wei Lin <tingweilin@google.com>
Reviewed-by: Hsu Wei-Cheng <mojahsu@chromium.org>

[modify] https://crrev.com/c7643491ecaef37e0b9ae24ac34039898dee6b39/overlay-sand/chromeos-base/chromeos-bsp-sand/chromeos-bsp-sand-0.0.1.ebuild
[rename] https://crrev.com/c7643491ecaef37e0b9ae24ac34039898dee6b39/overlay-sand/chromeos-base/chromeos-bsp-sand/chromeos-bsp-sand-0.0.1-r4.ebuild