Fix chromium-style compile error that got in the tree since yesterday.

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
 
@@ skipping 42 matching lines @@
   }
 
   // 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() {}
+  AboutTcmallocOutputs();
+  ~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_