Modify --log-net-log comment to remove option for command line output.

BUG=None
R=mmenke@chromium.org

Review URL: https://codereview.chromium.org/132283002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244204 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244204