Don't send mail for policy_checklist comments.

util.py

Index: util.py
diff --git a/util.py b/util.py
index 85c768777960278d6d923fc132355616238bdbb4..3eb5934d9b193c7c5716a42c59e908821fbfc102 100644
--- a/util.py
+++ b/util.py
@@ -86,3 +86,10 @@ def get_emails(string):
       [ 'test@example.com', 'committers@chromium.org' ]
   """
   return [entry[1] for entry in email.utils.getaddresses([string])]
+
+
+def canonicalize_email(address):
+  """Takes an email address and returns its canonicalized form."""
+  emails = get_emails(address)
+  assert len(emails) == 1
+  return emails[0]