Add a new GetInstance() method for singleton classes, take 2.

chrome_frame/policy_settings.h

 // Copyright (c) 2010 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_FRAME_POLICY_SETTINGS_H_
 #define CHROME_FRAME_POLICY_SETTINGS_H_
 
 #include <string>
 #include <vector>
+#include "base/singleton.h"
 
 #include "base/basictypes.h"
 
 // A simple class that reads and caches policy settings for Chrome Frame.
 // TODO(tommi): Support refreshing when new settings are pushed.
 // TODO(tommi): Use Chrome's classes for this (and the notification service).
 class PolicySettings {
  public:
   typedef enum RendererForUrl {
     RENDERER_NOT_SPECIFIED = -1,
     RENDER_IN_HOST,
     RENDER_IN_CHROME_FRAME,
   };
 
-  PolicySettings() : default_renderer_(RENDERER_NOT_SPECIFIED) {
-    RefreshFromRegistry();
-  }
-
-  ~PolicySettings() {
-  }
+  static PolicySettings* GetInstance();
 
   RendererForUrl default_renderer() const {
     return default_renderer_;
   }
 
   RendererForUrl GetRendererForUrl(const wchar_t* url);
 
   RendererForUrl GetRendererForContentType(const wchar_t* content_type);
 
   // Returns the policy-configured Chrome app locale, or an empty string if none
   // is configured.
   const std::wstring& ApplicationLocale() const {
     return application_locale_;
   }
 
   // Helper functions for reading settings from the registry
   static void ReadUrlSettings(RendererForUrl* default_renderer,
       std::vector<std::wstring>* renderer_exclusion_list);
   static void ReadContentTypeSetting(
       std::vector<std::wstring>* content_type_list);
   static void ReadApplicationLocaleSetting(std::wstring* application_locale);
 
  protected:
+  PolicySettings() : default_renderer_(RENDERER_NOT_SPECIFIED) {
+    RefreshFromRegistry();
+  }
+
+  ~PolicySettings() {
+  }
+
   // Protected for now since the class is not thread safe.
   void RefreshFromRegistry();
 
  protected:
   RendererForUrl default_renderer_;
   std::vector<std::wstring> renderer_exclusion_list_;
   std::vector<std::wstring> content_type_list_;
   std::wstring application_locale_;
 
  private:
+  // This ensures no construction is possible outside of the class itself.
+  friend struct DefaultSingletonTraits<PolicySettings>;
   DISALLOW_COPY_AND_ASSIGN(PolicySettings);
 };
 
-
 #endif  // CHROME_FRAME_POLICY_SETTINGS_H_