Clean up threading model of external extension providers

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 363 matching lines @@
         'annotations': {
           'features': {'dynamic_refresh': 1},
           'example_value': ['extension_id1', 'extension_id2']
         }
       },
       {
         'name': 'ExtensionInstallForcelist',
         'type': 'list',
         'supported_on': ['chrome.*:9-'],
         'annotations': {
-          'features': {'dynamic_refresh': 0},
+          'features': {'dynamic_refresh': 1},
           'example_value': [
             'lcncmkcnkcdbbanbjakcencbaoegdjlp;'
             'https://clients2.google.com/service/update2/crx'
           ]
         }
       }]
     },
     {
       'name': 'ShowHomeButton',
       'type': 'main',
@@ skipping 282 matching lines @@
     {
       'key': '$4',
       'value': 'http://www.chromium.org/developers/how-tos/chrome-frame-getting-started'
     },
     {
       'key': '$5',
       'value': 'http://www.chromium.org/administrators/policy-templates'
     },
   ]
 }