Check in pep8.py so that we don't auto-install it.

R=eseidel@chromium.org, ojan@chromium.org
BUG=230706

Review URL: https://chromiumcodereview.appspot.com/19481002

git-svn-id: svn://svn.chromium.org/blink/trunk@154360 bbb929c8-8fbe-4397-9dbb-9b2b20218538