crosperf: clean lint warnings.

BUG=chromium:567921
TEST=machine_manager.py is clean.

Change-Id: Ia3355ee78d15419ca531f358812f7882a64a6cbe
Reviewed-on: https://chrome-internal-review.googlesource.com/241491
Commit-Ready: Yunlian Jiang <yunlian@google.com>
Tested-by: Yunlian Jiang <yunlian@google.com>
Reviewed-by: Caroline Tice <cmtice@google.com>
3 files changed