cashew: fix cpplint errors in user_aggregator_unittest.cc

BUG=None
TEST=FEATURES=test emerge-${BOARD} cashew

Change-Id: I77572efc74ee9075e37a51a04f4707267ad71a6a
Reviewed-on: http://gerrit.chromium.org/gerrit/4945
Tested-by: Vince Laviano <vlaviano@chromium.org>
Reviewed-by: Michael Mekonnen <mikemeko@chromium.org>