Remove trailing periods from rule messages.

See commit message of r232166 for details.

BUG=none
NOTRY=true
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/130873002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243790 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243790