Pass the previous and the current PolicyMap to Observers of the PolicyService.

chrome/browser/policy/policy_service.h

 // 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.
 
 #ifndef CHROME_BROWSER_POLICY_POLICY_SERVICE_H_
 #define CHROME_BROWSER_POLICY_POLICY_SERVICE_H_
 #pragma once
 
 #include <string>
 
@@ skipping 16 matching lines @@
 //
 // The PolicyService is available from BrowserProcess as a global singleton.
 class PolicyService {
  public:
   class Observer {
    public:
     virtual ~Observer() {}
 
     // Invoked whenever policies for the |domain|, |component_id| namespace are
     // modified. This is only invoked for changes that happen after AddObserver
-    // is called.
+    // is called. |previous| contains the values of the policies before the
+    // update, and |current| contains the current values.
     virtual void OnPolicyUpdated(PolicyDomain domain,
-                                 const std::string& component_id) = 0;
+                                 const std::string& component_id,
+                                 const PolicyMap& previous,
+                                 const PolicyMap& current) = 0;
 
     // Invoked at most once, when the PolicyService becomes ready. If
     // IsInitializationComplete() is false, then this will be invoked once all
     // the policy providers are ready.
     virtual void OnPolicyServiceInitialized() {}
   };
 
   virtual ~PolicyService() {}
 
   virtual void AddObserver(PolicyDomain domain,
@@ skipping 18 matching lines @@
   // OnPolicyServiceInitialized() is called when IsInitializationComplete()
   // becomes true, which happens at most once. If IsInitializationComplete() is
   // already true when an Observer is registered, then that Observer will not
   // have a OnPolicyServiceInitialized() notification.
   virtual bool IsInitializationComplete() const = 0;
 };
 
 }  // namespace policy
 
 #endif  // CHROME_BROWSER_POLICY_POLICY_SERVICE_H_