Add a message that the list of directories needing owners may not be accurate on first upload, because we have no way to know whether the user is an OWNER for any of them.

BUG=117974
TEST=covered by presubmit unit tests

Review URL: http://codereview.chromium.org/9692039

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@126894 0039d316-1c4b-4281-b951-d872f2087c98