Add a new GetInstance() method for singleton classes used in chrome/browser files.

chrome/browser/browser_about_handler.h

 // Copyright (c) 2006-2008 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.
 
 // Contains code for handling "about:" URLs in the browser process.
 
 #ifndef CHROME_BROWSER_BROWSER_ABOUT_HANDLER_H_
 #define CHROME_BROWSER_BROWSER_ABOUT_HANDLER_H_
 #pragma once
 
 #include <map>
 #include <string>
 
 #include "base/process.h"
-#include "base/singleton.h"
 #include "base/string_util.h"
 
+template <typename T> struct DefaultSingletonTraits;
 class GURL;
 class Profile;
 
 // Decides whether the given URL will be handled by the browser about handler
 // and returns true if so. On true, it may also modify the given URL to be the
 // final form (we fix up most "about:" URLs to be "chrome:" because WebKit
 // handles all "about:" URLs as "about:blank.
 //
 // This is used by BrowserURLHandler.
 bool WillHandleBrowserAboutURL(GURL* url, Profile* profile);
 
 // We have a few magic commands that don't cause navigations, but rather pop up
 // dialogs. This function handles those cases, and returns true if so. In this
 // case, normal tab navigation should be skipped.
 bool HandleNonNavigationAboutURL(const GURL& url);
 
 #if defined(USE_TCMALLOC)
 // A map of header strings (e.g. "Browser", "Renderer PID 123")
 // to the tcmalloc output collected for each process.
 typedef std::map<std::string, std::string> AboutTcmallocOutputsType;
 
 class AboutTcmallocOutputs {
  public:
-  AboutTcmallocOutputs() {}
+  // Returns the singleton instance.
+  static AboutTcmallocOutputs* GetInstance();
 
   AboutTcmallocOutputsType* outputs() { return &outputs_; }
 
   // Records the output for a specified header string.
   void SetOutput(std::string header, std::string output) {
     outputs_[header] = output;
   }
 
   // Callback for output returned from renderer processes.  Adds
   // the output for a canonical renderer header string that
   // incorporates the pid.
   void RendererCallback(base::ProcessId pid, std::string output) {
     SetOutput(StringPrintf("Renderer PID %d", static_cast<int>(pid)), output);
   }
 
  private:
+  AboutTcmallocOutputs() {}
+
   AboutTcmallocOutputsType outputs_;
 
   friend struct DefaultSingletonTraits<AboutTcmallocOutputs>;
 
   DISALLOW_COPY_AND_ASSIGN(AboutTcmallocOutputs);
 };
 
 // Glue between the callback task and the method in the singleton.
 void AboutTcmallocRendererCallback(base::ProcessId pid, std::string output);
 #endif
 
 #endif  // CHROME_BROWSER_BROWSER_ABOUT_HANDLER_H_