There are several places where we advise people
to use custom_deps with { "foo" : None } to avoid
checking out certain sub-repos.  This caused wtf to
crash on startup.


BUG=


Review URL: https://chromiumcodereview.appspot.com/10917220

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@156373 0039d316-1c4b-4281-b951-d872f2087c98