Reset user data directory and disk cache directory after downgrade.

components/policy/resources/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 1393 matching lines @@
       'features': {
         'dynamic_refresh': False,
         'per_profile': False,
       },
       'example_value': '${users}/${user_name}/Chrome',
       'id': 63,
       'caption': '''Set user data directory''',
       'tags': ['local-data-access'],
       'desc': '''Configures the directory that <ph name="PRODUCT_NAME">$1<ex>Google Chrome</ex></ph> will use for storing user data.
 
-      If you set this policy, <ph name="PRODUCT_NAME">$1<ex>Google Chrome</ex></ph> will use the provided directory regardless whether the user has specified the '--user-data-dir' flag or not.
+      If you set this policy, <ph name="PRODUCT_NAME">$1<ex>Google Chrome</ex></ph> will use the provided directory regardless whether the user has specified the '--user-data-dir' flag or not. To avoid data loss or other unexpected errors this policy should not be set to a volume's root directory or to a directory used for other purposes, because <ph name="PRODUCT_NAME">$1<ex>Google Chrome</ex></ph> manages its contents.
 
       See https://www.chromium.org/administrators/policy-list-3/user-data-directory-variables for a list of variables that can be used.
 
       If this policy is left not set the default profile path will be used and the user will be able to override it with the '--user-data-dir' command line flag.''',
       'label': '''Set user data directory''',
     },
     {
       'name': 'DiskCacheDir',
       'type': 'string',
       'schema': { 'type': 'string' },
       'supported_on': ['chrome.*:13-'],
       'features': {
         'dynamic_refresh': False,
         'per_profile': False,
       },
       'example_value': '${user_home}/Chrome_cache',
       'id': 88,
       'caption': '''Set disk cache directory''',
       'tags': [],
       'desc': '''Configures the directory that <ph name="PRODUCT_NAME">$1<ex>Google Chrome</ex></ph> will use for storing cached files on the disk.
 
-      If you set this policy, <ph name="PRODUCT_NAME">$1<ex>Google Chrome</ex></ph> will use the provided directory regardless whether the user has specified the '--disk-cache-dir' flag or not.
+      If you set this policy, <ph name="PRODUCT_NAME">$1<ex>Google Chrome</ex></ph> will use the provided directory regardless whether the user has specified the '--disk-cache-dir' flag or not. To avoid data loss or other unexpected errors this policy should not be set to a volume's root directory or to a directory used for other purposes, because <ph name="PRODUCT_NAME">$1<ex>Google Chrome</ex></ph> manages its contents.
 
       See https://www.chromium.org/administrators/policy-list-3/user-data-directory-variables for a list of variables that can be used.
 
       If this policy is left not set the default cache directory will be used and the user will be able to override it with the '--disk-cache-dir' command line flag.''',
       'label': '''Set disk cache directory''',
     },
     {
       'name': 'DiskCacheSize',
       'type': 'int',
       'schema': { 'type': 'integer' },
@@ skipping 7291 matching lines @@
       '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)',
     },
     'doc_complex_policies_on_windows': {
       'desc': '''Text pointing the user to a help article for complex policies on Windows''',
       'text': '''encoded as a JSON string, for details see <ph name="COMPLEX_POLICIES_URL">https://www.chromium.org/administrators/complex-policies-on-windows<ex>https://www.chromium.org/administrators/complex-policies-on-windows</ex></ph>''',
     },
   },
   'placeholders': [],
 }