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

win8/metro_driver/chrome_app_view_ash.cc

Index: win8/metro_driver/chrome_app_view_ash.cc
diff --git a/win8/metro_driver/chrome_app_view_ash.cc b/win8/metro_driver/chrome_app_view_ash.cc
index 79649ffeae9e46b6aa86833783e8a1f3e12f1e42..c978d8eb13b9a85deaf9586674cd50c990ec7def 100644
--- a/win8/metro_driver/chrome_app_view_ash.cc
+++ b/win8/metro_driver/chrome_app_view_ash.cc
@@ -157,6 +157,7 @@ class ChromeChannelListener : public IPC::Listener {
     IPC_BEGIN_MESSAGE_MAP(ChromeChannelListener, message)
       IPC_MESSAGE_HANDLER(MetroViewerHostMsg_ActivateDesktop,
                           OnActivateDesktop)
+      IPC_MESSAGE_HANDLER(MetroViewerHostMsg_MetroExit, OnMetroExit)
       IPC_MESSAGE_HANDLER(MetroViewerHostMsg_OpenURLOnDesktop,
                           OnOpenURLOnDesktop)
       IPC_MESSAGE_HANDLER(MetroViewerHostMsg_SetCursor, OnSetCursor)
@@ -194,6 +195,10 @@ class ChromeChannelListener : public IPC::Listener {
         shortcut, ash_exit));
   }
 
+  void OnMetroExit() {
+    MetroExit(app_view_->core_window_hwnd());
+  }
+
   void OnOpenURLOnDesktop(const base::FilePath& shortcut,
                           const base::string16& url) {
     ui_proxy_->PostTask(FROM_HERE,