Unit test for queue implementation

BUG=chrome-os-partner:19236
TEST=Pass the test.
BRANCH=None

Change-Id: I575e4a9abfd9431e3b74c36da8c3d69285e5c0fb
Signed-off-by: Vic Yang <victoryang@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/58032
Reviewed-by: Yung-Chieh Lo <yjlou@chromium.org>