Add the flag module.

BUG=None
TEST=unit testings for the pipeline stage, pipeline workers, generation,
steering, task and flag.

Change-Id: Ia1b32f859da2fc0984b940393b688a44221f3611
Reviewed-on: https://gerrit-int.chromium.org/41847
Reviewed-by: Simon Que <sque@google.com>
Reviewed-by: Luis Lozano <llozano@chromium.org>
Commit-Queue: Yuheng Long <yuhenglong@google.com>
Tested-by: Yuheng Long <yuhenglong@google.com>
2 files changed