Added PolicyChangeRegistrar, to observe specific policies at 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 5b5f3f33507a61bb6a964191b3c4571bca07e9bd..db76668d4ed198b9e86636b61efda772313ca867 100644
--- a/chrome/browser/policy/policy_service.h
+++ b/chrome/browser/policy/policy_service.h
@@ -6,8 +6,10 @@
 #define CHROME_BROWSER_POLICY_POLICY_SERVICE_H_
 #pragma once
 
+#include <set>
 #include <string>
 
+#include "base/basictypes.h"
 #include "chrome/browser/policy/policy_map.h"
 
 namespace policy {
@@ -75,6 +77,59 @@ class PolicyService {
   virtual bool IsInitializationComplete() const = 0;
 };
 
+// A registrar that only observes changes to particular policies within the
+// PolicyMap for the given policy namespace.
+class PolicyChangeRegistrar : public PolicyService::Observer {
+ public:
+  class Observer {
+   public:
+     virtual ~Observer() {}
+
+    // Invoked whenever the given |policy_name| changes within the
+    // (domain, component_id) namespace. Both the previous and the current
+    // values are provided; either can be NULL.
+    virtual void OnPolicyValueUpdated(PolicyDomain domain,
+                                      const std::string& component_id,
+                                      const std::string& policy_name,
+                                      const Value* previous_value,
+                                      const Value* current_value) = 0;
+  };
+
+  // Observes updates to the given (domain, component_id) namespace in the given
+  // |policy_service|, and notifies |observer| whenever any of the registered
+  // policy keys changes. Both the |policy_service| and the |observer| must
+  // outlive |this|.
+  PolicyChangeRegistrar(PolicyService* policy_service,
+                        PolicyDomain domain,
+                        const std::string component_id,
+                        Observer* observer);
+
+  ~PolicyChangeRegistrar();
+
+  // Adds |policy_name| to the set of policies to observe.
+  void Add(const std::string& policy_name);
+
+  // Removes |policy_name| from the set of policies to observe. The destructor
+  // unregisters |this| as an observer of the |policy_service_|, and it's not
+  // necessary to Remove() the policies that were added before deleting |this|.
+  void Remove(const std::string& policy_name);
+
+  // Implementation of PolicyService::Observer:
+  virtual void OnPolicyUpdated(PolicyDomain domain,
+                               const std::string& component_id,
+                               const PolicyMap& previous,
+                               const PolicyMap& current) OVERRIDE;
+
+ private:
+  PolicyService* policy_service_;
+  PolicyDomain domain_;
+  std::string component_id_;
+  Observer* observer_;

[Mattias Nissler (ping if slow), 2012/04/23 15:42:50]

How about making this a base::Callback?

[Joao da Silva, 2012/04/23 16:52:28]

Done. I've mapped a callback per policy name, so that the callback only takes
the old/new values and doesn't need the policy_name too, and the invoked
function doesn't have to "switch" on the policy_name. Users of the registrar can
always bind that information to the callback, if they want to receive it. wdyt?

+  std::set<std::string> observing_;

[Mattias Nissler (ping if slow), 2012/04/23 15:42:50]

Could use a better name, observed_policies_ for example.

+
+  DISALLOW_COPY_AND_ASSIGN(PolicyChangeRegistrar);
+};
+
 }  // namespace policy
 
 #endif  // CHROME_BROWSER_POLICY_POLICY_SERVICE_H_