This is useful to diagnose slow tests. Make this multiprocessing aware. Stop
printing when the commands are added but use the proper message system instead.

R=iannucci@chromium.org
BUG=

Review URL: https://codereview.chromium.org/99453003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@238388 0039d316-1c4b-4281-b951-d872f2087c98