Make the hcsm and its providers communicate via an observer interface.

chrome/browser/content_settings/content_settings_policy_provider.h

 // Copyright (c) 2011 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_CONTENT_SETTINGS_CONTENT_SETTINGS_POLICY_PROVIDER_H_
 #define CHROME_BROWSER_CONTENT_SETTINGS_CONTENT_SETTINGS_POLICY_PROVIDER_H_
 #pragma once
 
 // A content settings provider that takes its settings out of policies.
 
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/synchronization/lock.h"
 #include "base/tuple.h"
 #include "chrome/browser/content_settings/content_settings_origin_identifier_value_map.h"
-#include "chrome/browser/content_settings/content_settings_provider.h"
+#include "chrome/browser/content_settings/content_settings_abstract_provider.h"
 #include "chrome/browser/prefs/pref_change_registrar.h"
 #include "content/common/notification_observer.h"
 #include "content/common/notification_registrar.h"
 
 class ContentSettingsDetails;
 class DictionaryValue;
 class HostContentSettingsMap;
 class PrefService;
 
 namespace content_settings {
@@ skipping 43 matching lines @@
   // guarantee thread safety.
   mutable base::Lock lock_;
 
   PrefChangeRegistrar pref_change_registrar_;
   NotificationRegistrar notification_registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(PolicyDefaultProvider);
 };
 
 // PolicyProvider that provider managed content-settings.
-class PolicyProvider : public ProviderInterface,
+class PolicyProvider : public AbstractProvider,
                        public NotificationObserver {
  public:
-  PolicyProvider(HostContentSettingsMap* map,
+  PolicyProvider(Observer* observer,

[Bernhard Bauer, 2011/07/13 13:21:28]

Come to think of it, do we actually *need* an observer in the constructor? If an
ObservableProvider has an arbitrary number of observers (as opposed to exactly
one), it should also be possible to have zero (like for the unit test case).

[markusheintz_, 2011/07/13 13:28:53]

That is totally correct!

Basically the host content settings map need to call AddObserver(this) after
creating a content setting provider and RemoveObserver(this) when it is 
shutdown.

I implemented this originally and I'm very in favor of that solution.

I will also have to change the ProviderPtr type in the HostContentSettingsMap to
point the an ObservableProvider (AbstractProvider)

[Bernhard Bauer, 2011/07/13 13:41:32]

No, you don't. At the point where you create the concrete Provider, you know its
exact type, so you can call ObservableProvider methods on it, but the elements
of the provider list only need to be of type Provider.

[markusheintz_, 2011/07/13 14:14:42]

Ok.

                  PrefService* prefs,
                  DefaultProviderInterface* default_provider);
   virtual ~PolicyProvider();
   static void RegisterUserPrefs(PrefService* prefs);
 
-  // ProviderInterface Implementation
+  // ProviderInterface implementations.
   virtual void SetContentSetting(
       const ContentSettingsPattern& primary_pattern,
       const ContentSettingsPattern& secondary_pattern,
       ContentSettingsType content_type,
       const ResourceIdentifier& resource_identifier,
       ContentSetting content_setting);
 
   virtual ContentSetting GetContentSetting(
       const GURL& primary_url,
       const GURL& secondary_url,
@@ skipping 23 matching lines @@
       ContentSetting> ContentSettingsRule;
 
   typedef std::vector<ContentSettingsRule> ContentSettingsRules;
 
   void ReadManagedContentSettings(bool overwrite);
 
   void GetContentSettingsFromPreferences(ContentSettingsRules* rules);
 
   void ReadManagedContentSettingsTypes(ContentSettingsType content_type);
 
-  void NotifyObservers(const ContentSettingsDetails& details);
-
   OriginIdentifierValueMap value_map_;
 
-  HostContentSettingsMap* host_content_settings_map_;
   PrefService* prefs_;
 
   // Weak, owned by HostContentSettingsMap.
   DefaultProviderInterface* default_provider_;
 
   PrefChangeRegistrar pref_change_registrar_;
 
   // Used around accesses to the content_settings_ object to guarantee
   // thread safety.
   mutable base::Lock lock_;
 
   DISALLOW_COPY_AND_ASSIGN(PolicyProvider);
 };
 
 }  // namespace content_settings
 
 #endif  // CHROME_BROWSER_CONTENT_SETTINGS_CONTENT_SETTINGS_POLICY_PROVIDER_H_