Have browser process shutdown metro viewer on Metro -> Metro restart.

chrome/browser/browser_process_platform_part_aurawin.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_AURAWIN_H_
 #define CHROME_BROWSER_BROWSER_PROCESS_PLATFORM_PART_AURAWIN_H_
 
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/browser_process_platform_part_base.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
 
 class ChromeMetroViewerProcessHost;
 
-class BrowserProcessPlatformPart : public BrowserProcessPlatformPartBase {
+class BrowserProcessPlatformPart : public BrowserProcessPlatformPartBase,
+                                   public content::NotificationObserver {
  public:
   BrowserProcessPlatformPart();
   virtual ~BrowserProcessPlatformPart();
 
   // Invoked when the ASH metro viewer process on Windows 8 exits.
   void OnMetroViewerProcessTerminated();
 
   // Overridden from BrowserProcessPlatformPartBase:
   virtual void PlatformSpecificCommandLineProcessing(
       const CommandLine& command_line) OVERRIDE;
 
+  // content::NotificationObserver method:
+  virtual void Observe(int type,
+                       const content::NotificationSource& source,
+                       const content::NotificationDetails& details) OVERRIDE;
+
  private:
   // Hosts the channel for the Windows 8 metro viewer process which runs in
   // the ASH environment.
   scoped_ptr<ChromeMetroViewerProcessHost> metro_viewer_process_host_;
 
+  content::NotificationRegistrar registrar_;
+
   DISALLOW_COPY_AND_ASSIGN(BrowserProcessPlatformPart);
 };
 
 #endif  // CHROME_BROWSER_BROWSER_PROCESS_PLATFORM_PART_AURAWIN_H_