toolchain-utils: fix class-missing-docstring lint warnings.

BUG=chromium:570458
TEST='crosperf/run_tests.sh' passes.

Change-Id: I0640cab2c8d15380badbfbc0db39e3063cc85471
Reviewed-on: https://chrome-internal-review.googlesource.com/244867
Commit-Ready: Rahul Chaudhry <rahulchaudhry@google.com>
Tested-by: Rahul Chaudhry <rahulchaudhry@google.com>
Reviewed-by: Luis Lozano <llozano@chromium.org>
14 files changed