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

chrome/browser/policy/policy_service.h

Index: chrome/browser/policy/policy_service.h
diff --git a/chrome/browser/policy/policy_service.h b/chrome/browser/policy/policy_service.h
index 124c41c0007f4764c6dcabb92d380714cd015dcb..5b5f3f33507a61bb6a964191b3c4571bca07e9bd 100644
--- a/chrome/browser/policy/policy_service.h
+++ b/chrome/browser/policy/policy_service.h
@@ -34,9 +34,12 @@ class PolicyService {
 
     // 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