crosperf: fix lint warnings.

BUG=chromium:570454
TEST=unittest passes, lint warning is gone.

Change-Id: I37f71a1195454657f205845d346b5ad76be878ec
Reviewed-on: https://chrome-internal-review.googlesource.com/243141
Commit-Ready: Yunlian Jiang <yunlian@google.com>
Tested-by: Yunlian Jiang <yunlian@google.com>
Reviewed-by: Luis Lozano <llozano@chromium.org>
2 files changed