Deprecated HideWebStorePromo policy and updated the pyauto test case for it.

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 2385 matching lines @@
       The value of this policy should be lower than 100 and higher than 6 and the default value is 32.
 
       Some web apps are known to consume many connections with hanging GETs, so lowering below 32 may lead to browser networking hangs if too many such web apps are open. Lower below the default at your own risk.
 
       If this policy is left not set the default value will be used which is 32.''',
     },
     {
       'name': 'HideWebStorePromo',
       'type': 'main',
       'schema': { 'type': 'boolean' },
-      'supported_on': ['chrome.*:15-', 'chrome_os:0.15-'],
+      'supported_on': ['chrome.*:15-21', 'chrome_os:0.15-21'],
+      'deprecated': True,
       'features': {'dynamic_refresh': False},
       'example_value': False,
       'id': 96,
       'caption': '''Prevent app promotions from appearing on the new tab page''',
       'desc': '''When set to True, promotions for Chrome Web Store apps will not appear on the new tab page.
 
       Setting this option to False or leaving it not set will make the promotions for Chrome Web Store apps appear on the new tab page''',
     },
     {
       'name': 'URLBlacklist',
@@ skipping 774 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': 'Recommended',
     },
   },
   'placeholders': [],
 }