Login screen and Guest mode should use device owner preference

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 99 matching lines @@
 #   templates and documentation. The policy definition list that Chrome sees
 #   will include policies marked with 'future'. If a WIP policy isn't meant to
 #   be seen by the policy providers either, the 'supported_on' key should be set
 #   to an empty list.
 #
 # IDs:
 #   Since a Protocol Buffer definition is generated from this file, unique and
 #   persistent IDs for all fields (but not for groups!) are needed. These are
 #   specified by the 'id' keys of each policy. NEVER CHANGE EXISTING IDs,
 #   because doing so would break the deployed wire format!
-#   For your editing convenience: highest ID currently used: 235
+#   For your editing convenience: highest ID currently used: 236
 #
 # Placeholders:
 #   The following placeholder strings are automatically substituted:
 #     $1 -> Google Chrome / Chromium
 #     $2 -> Google Chrome OS / Chromium OS
 #     $3 -> Google Chrome Frame / Chromium Frame
 #     $6 is reserved for doc_writer
 #
 # Device Policy:
 #   An additional flag device_only (optional, defaults to False) indicates
@@ skipping 3927 matching lines @@
       'caption': '''Timezone''',
       'desc': '''Specifies the timezone to be used for the device. Users can override the specified timezone for the current session. However, on logout it is set back to the specified timezone. If an invalid value is provided, the policy is still activated using "GMT" instead. If an empty string is provided, the policy is ignored.
 
       If this policy is not used, the currently active timezone will remain in use however users can change the timezone and the change is persistent. Thus a change by one user affects the login-screen and all other users.
 
       New devices start out with the timezone set to "US/Pacific".
 
       The format of the value follows the names of timezones in the "IANA Time Zone Database" (see "http://en.wikipedia.org/wiki/List_of_tz_database_time"). In particular, most timezones can be referred to by "continent/large_city" or "ocean/large_city".''',
     },
     {
+      'name': 'SystemUse24HourClock',
+      'type': 'main',
+      'schema': { 'type': 'boolean' },
+      'supported_on': ['chrome_os:30-'],
+      'device_only': True,
+      'features': {
+        'dynamic_refresh': True,
+      },
+      'example_value': True,
+      'id': 236,
+      'caption': '''Use 24 hour clock by default''',
+      'desc': '''Specifies the clock format be used for the device. Users can override clock format for the current session. However, on logout it is set back to the specified value. If an empty string is provided, device owner preference is used.''',
+    },
+    {
       'name': 'ShowLogoutButtonInTray',
       'type': 'main',
       'schema': { 'type': 'boolean' },
       'supported_on': ['chrome_os:25-'],
       'features': {
         'dynamic_refresh': True,
         'per_profile': True,
       },
       'example_value': True,
       'id': 164,
@@ skipping 1453 matching lines @@
       'desc': '''Text appended in parentheses to the policy name to indicate that it has been deprecated''',
       'text': 'deprecated',
     },
     'doc_recommended': {
       'desc': '''Text appended in parentheses next to the policies top-level container to indicate that those policies are of the Recommended level''',
       'text': 'Default Settings (users can override)',
     },
   },
   'placeholders': [],
 }