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

chrome/browser/browser_process_platform_part_winaura.h

Index: chrome/browser/browser_process_platform_part_winaura.h
diff --git a/chrome/browser/browser_process_platform_part_winaura.h b/chrome/browser/browser_process_platform_part_winaura.h
index db3d5dcdca53613d0f7dc3df8ce9cf157e68ed1c..04b47b60bff0169ebcbdb194a0d110cae3bef28e 100644
--- a/chrome/browser/browser_process_platform_part_winaura.h
+++ b/chrome/browser/browser_process_platform_part_winaura.h
@@ -24,8 +24,12 @@ class BrowserProcessPlatformPart {
   // Called from BrowserProcessImpl::StartTearDown().
   virtual void StartTearDown();
 
+  // Invoked when the ASH metro viewer process on Windows 8 exits.
   void OnMetroViewerProcessTerminated();
 
+  // Terminates the metro viewer process if there is one.
+  void TerminateMetroViewerProcess();
+
  private:
   // Hosts the channel for the Windows 8 metro viewer process which runs in
   // the ASH environment.