In WinAura, also kill the Metro viewer process in AttemptExit().

chrome/browser/browser_process_platform_part_base.h

 // Copyright (c) 2013 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_BROWSER_PROCESS_PLATFORM_PART_BASE_H_
 #define CHROME_BROWSER_BROWSER_PROCESS_PLATFORM_PART_BASE_H_
 
 #include "base/basictypes.h"
 
 class CommandLine;
 
 // A base class for platform-specific BrowserProcessPlatformPart
 // implementations. This class itself should never be used verbatim.
 class BrowserProcessPlatformPartBase {
  public:
   BrowserProcessPlatformPartBase();
   virtual ~BrowserProcessPlatformPartBase();
 
   // Called after creating the process singleton or when another chrome
   // rendez-vous with this one.
   virtual void PlatformSpecificCommandLineProcessing(
       const CommandLine& command_line);
 
   // Called from BrowserProcessImpl::StartTearDown().
   virtual void StartTearDown();
 
+  // Called from AttemptExitInternal().
+  virtual void AttemptExit();
+
  private:
   DISALLOW_COPY_AND_ASSIGN(BrowserProcessPlatformPartBase);
 };
 
 #endif  // CHROME_BROWSER_BROWSER_PROCESS_PLATFORM_PART_BASE_H_