Add preference for managed notifications setting.

chrome/app/policy/policy_templates.json

 {
 # policy_templates.json - Metafile for policy templates
 #
 # The content of this file is evaluated as a Python expression.
 #
 # This file is used as input to generate the following policy templates:
 # ADM, ADMX+ADML, MCX/plist and html documentation.
 #
 # Policy templates are user interface definitions or documents about the
 # policies that can be used to configure Chrome. Each policy is a name-value
@@ skipping 1200 matching lines @@
             },
           ],
           'supported_on': ['chrome.*:10-', 'chrome_os:0.11-'],
           'features': {'dynamic_refresh': 1},
           'example_value': 1,
           'id': 52,
           'caption': '''Default popups setting''',
           'desc': '''Allows you to set whether websites are allowed to show pop-ups. Showing popups can be either allowed for all websites or denied for all websites.''',
         },
         {
-          'name': 'DefaultNotificationSetting',
+          'name': 'DefaultNotificationsSetting',
           'type': 'int-enum',
           'items': [
             {
               'name': 'AllowNotifications',
               'value': 1,
               'caption': '''Allow sites to show desktop notifications'''
             },
             {
               'name': 'BlockNotifications',
               'value': 2,
@@ skipping 534 matching lines @@
       'desc': '''The name of the feature that indicates for a given policy that changes to it are respected by Chrome without a browser restart''',
       'text': '''Dynamic Policy Refresh'''
     },
     'doc_deprecated': {
       'desc': '''Text appended in parentheses to the policy name to indicate t hat it has been deprecated''',
       'text': 'deprecated',
     }
   },
   'placeholders': [],
 }