Clean up threading model of external extension providers

chrome/browser/extensions/external_policy_extension_loader.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_EXTENSIONS_EXTERNAL_POLICY_EXTENSION_LOADER_H_
+#define CHROME_BROWSER_EXTENSIONS_EXTERNAL_POLICY_EXTENSION_LOADER_H_
+#pragma once
+
+#include "chrome/browser/extensions/external_extension_loader.h"
+
+#include "chrome/browser/prefs/pref_change_registrar.h"
+#include "chrome/common/notification_observer.h"
+#include "chrome/common/notification_registrar.h"
+
+class ListValue;
+class MockExternalPolicyExtensionProviderVisitor;
+class Profile;
+
+// A specialization of the ExternalExtensionProvider that uses
+// prefs::kExtensionInstallForceList to look up which external extensions are
+// registered.
+class ExternalPolicyExtensionLoader
+    : public ExternalExtensionLoader,
+      public NotificationObserver {
+ public:
+  explicit ExternalPolicyExtensionLoader(Profile* profile);
+
+  // NotificationObserver implementation
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
+
+ protected:
+  virtual void StartLoading();
+
+ private:
+  friend class base::RefCountedThreadSafe<ExternalExtensionLoader>;
+
+  virtual ~ExternalPolicyExtensionLoader() {}
+
+  PrefChangeRegistrar pref_change_registrar_;
+  NotificationRegistrar notification_registrar_;
+
+  Profile* profile_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExternalPolicyExtensionLoader);
+};
+
+#endif  // CHROME_BROWSER_EXTENSIONS_EXTERNAL_POLICY_EXTENSION_LOADER_H_