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

ui/aura/remote_root_window_host_win.cc

Index: ui/aura/remote_root_window_host_win.cc
diff --git a/ui/aura/remote_root_window_host_win.cc b/ui/aura/remote_root_window_host_win.cc
index 5628e134aefa7a531cd36646ffdaa2941c2a1a7c..146133829ee61b1ddc9a9a7454f4246bca7baf4b 100644
--- a/ui/aura/remote_root_window_host_win.cc
+++ b/ui/aura/remote_root_window_host_win.cc
@@ -142,6 +142,11 @@ void HandleActivateDesktop(const base::FilePath& shortcut,
                                                                    ash_exit);
 }
 
+void HandleMetroExit() {
+  DCHECK(aura::RemoteWindowTreeHostWin::Instance());
+  aura::RemoteWindowTreeHostWin::Instance()->HandleMetroExit();
+}
+
 RemoteWindowTreeHostWin* g_instance = NULL;
 
 RemoteWindowTreeHostWin* RemoteWindowTreeHostWin::Instance() {
@@ -249,6 +254,12 @@ void RemoteWindowTreeHostWin::HandleActivateDesktop(
   host_->Send(new MetroViewerHostMsg_ActivateDesktop(shortcut, ash_exit));
 }
 
+void RemoteWindowTreeHostWin::HandleMetroExit() {
+  if (!host_)
+    return;
+  host_->Send(new MetroViewerHostMsg_MetroExit());
+}
+
 void RemoteWindowTreeHostWin::HandleOpenFile(
     const base::string16& title,
     const base::FilePath& default_path,