Refactor FileBasedPolicyProvider, introduce AsynchronousPolicyProvider.

chrome/browser/policy/configuration_policy_provider.h

 // Copyright (c) 2010 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.
 
 #ifndef CHROME_BROWSER_POLICY_CONFIGURATION_POLICY_PROVIDER_H_
 #define CHROME_BROWSER_POLICY_CONFIGURATION_POLICY_PROVIDER_H_
 #pragma once
 
 #include <string>
 #include <vector>
@@ skipping 35 matching lines @@
   // |Apply| method of |store| to apply specific policies.
   // Returns true if the policy could be provided, otherwise false.
   virtual bool Provide(ConfigurationPolicyStoreInterface* store) = 0;
 
   // Called by the subclass provider at any time to indicate that the currently
   // applied policy is not longer current. A policy refresh will be initiated as
   // soon as possible.
   virtual void NotifyStoreOfPolicyChange();
 
   // Decodes the value tree and writes the configuration to the given |store|.
-  void DecodePolicyValueTree(DictionaryValue* policies,
+  void DecodePolicyValueTree(const DictionaryValue* policies,
                              ConfigurationPolicyStoreInterface* store);
  protected:
   const PolicyDefinitionList* policy_definition_list() const {
     return policy_definition_list_;
   }
 
  private:
   // Contains the default mapping from policy values to the actual names.
   const ConfigurationPolicyProvider::PolicyDefinitionList*
       policy_definition_list_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ConfigurationPolicyProvider);
 };
 
 }  // namespace policy
 
 #endif  // CHROME_BROWSER_POLICY_CONFIGURATION_POLICY_PROVIDER_H_