Add 3 unittests, for test_flag.py, config.py and benchmark.py

BUG=None
TEST=Ran unittests.

Change-Id: I2c421f8322e58173932656da9ae7a5af1bf3febd
Reviewed-on: https://chrome-internal-review.googlesource.com/162886
Reviewed-by: Yunlian Jiang <yunlian@google.com>
Commit-Queue: Caroline Tice <cmtice@google.com>
Tested-by: Caroline Tice <cmtice@google.com>
3 files changed