Add support for Chrome policy type that references external data

grit/format/policy_templates/writers/adml_writer.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from xml.dom import minidom
 from grit.format.policy_templates.writers import xml_formatted_writer
 
 
 def GetWriter(config):
@@ skipping 90 matching lines @@
       dropdownlist_elem.appendChild(self._doc.createTextNode(policy_label))
     elif policy_type == 'list':
       self._AddString(self._string_table_elem,
                       policy_name + 'Desc',
                       policy_caption)
       listbox_elem = self.AddElement(presentation_elem, 'listBox',
                                      {'refId': policy_name + 'Desc'})
       listbox_elem.appendChild(self._doc.createTextNode(policy_label))
     elif policy_type == 'group':
       pass
+    elif policy_type == 'external':
+      # This type can only be set through cloud policy.
+      pass
     else:
       raise Exception('Unknown policy type %s.' % policy_type)
 
   def BeginPolicyGroup(self, group):
     '''Generates ADML elements for a Policy-Group. For each Policy-Group two
     ADML "string" elements are added to the string-table. One contains the
     caption of the Policy-Group and the other a description. A Policy-Group also
     requires an ADML "presentation" element that must be added to the
     presentation-table. The "presentation" element is the container for the
     elements that define the visual presentation of the Policy-Goup's Policies.
@@ skipping 50 matching lines @@
     self._presentation_table_elem = self.AddElement(resources_elem,
                                                    'presentationTable')
 
   def GetTemplateText(self):
     # Using "toprettyxml()" confuses the Windows Group Policy Editor
     # (gpedit.msc) because it interprets whitespace characters in text between
     # the "string" tags. This prevents gpedit.msc from displaying the category
     # names correctly.
     # TODO(markusheintz): Find a better formatting that works with gpedit.
     return self._doc.toxml()