Check in the coverage module from pypi so that we don't have to auto-install it.

R=ojan@chromium.org
BUG=230706

Review URL: https://codereview.chromium.org/19688003

git-svn-id: svn://svn.chromium.org/blink/trunk@154464 bbb929c8-8fbe-4397-9dbb-9b2b20218538