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

ui/aura/remote_root_window_host_win.h

Index: ui/aura/remote_root_window_host_win.h
diff --git a/ui/aura/remote_root_window_host_win.h b/ui/aura/remote_root_window_host_win.h
index a295109a8d5ab8f9f76a0265364b1e564e4da691..b589534e6ef1063d7f20fc23671f5dacfda039d4 100644
--- a/ui/aura/remote_root_window_host_win.h
+++ b/ui/aura/remote_root_window_host_win.h
@@ -86,14 +86,17 @@ AURA_EXPORT void HandleSelectFolder(const base::string16& title,
                                     const SelectFolderCompletion& on_success,
                                     const FileSelectionCanceled& on_failure);
 
-// Handles the activate desktop command for Metro Chrome Ash. The on_success
-// callback passed in is invoked when activation is completed.
-// The |ash_exit| parameter indicates whether the Ash process would be shutdown
-// after activating the desktop.
+// Handles the activate desktop command for Metro Chrome Ash.   The |ash_exit|
+// parameter indicates whether the Ash process would be shutdown after
+// activating the desktop.
 AURA_EXPORT void HandleActivateDesktop(
     const base::FilePath& shortcut,
     bool ash_exit);
 
+// Handles the metro exit command.  Causes the metro viewer to close itself
+// gracefully.
+AURA_EXPORT void HandleMetroExit();

[sky, 2014/01/09 16:40:05]

Why do we need this instead of having callers do
aura::RemoteRootWindowHostWin::Instance()->HandleMetroExit(); ? I suppose this
question applies to all the Hande functions here. Also, why do these have
'Handle' in them? ExitMetro() would be a lot clearer name for this.

[zturner, 2014/01/10 19:00:26]

I believe it's because on component builds we have aura.dll, which hosts
RemoteRootWindowHostWin, so we need to call an exported function.

As for the Handle, I'm not sure.  I left it for consistency, but I can change it
if you feel strongly.  These are basically one-to-one mappings which translate
into "Send an IPC to the Metro Viewer that does X"

+
 // RootWindowHost implementaton that receives events from a different
 // process. In the case of Windows this is the Windows 8 (aka Metro)
 // frontend process, which forwards input events to this class.
@@ -121,9 +124,9 @@ class AURA_EXPORT RemoteRootWindowHostWin
 
   // The |ash_exit| parameter indicates whether the Ash process would be
   // shutdown after activating the desktop.
-  void HandleActivateDesktop(
-      const base::FilePath& shortcut,
-      bool ash_exit);
+  void HandleActivateDesktop(const base::FilePath& shortcut, bool ash_exit);
+
+  void HandleMetroExit();
 
   void HandleOpenFile(const base::string16& title,
                       const base::FilePath& default_path,