Minor documentation fixup, followup from https://codereview.chromium.org/184903003

BUG=308843
NOTRY=true

Review URL: https://codereview.chromium.org/195893015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257053 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257053