ash: Add RootWindowHostFactory class.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 346c9775ba1373aec049ad65be55f02d9f403ae5..187441a57229b1182247a58604241796021ada3a 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "ash/ash_export.h"
+#include "ash/display/display_manager_delegate.h"
 #include "ash/shelf_types.h"
 #include "ash/system/user/login_status.h"
 #include "ash/wm/cursor_manager.h"
@@ -125,6 +126,7 @@ class ShellTestApi;
 // Upon creation, the Shell sets itself as the RootWindow's delegate, which
 // takes ownership of the Shell.
 class ASH_EXPORT Shell : internal::SystemModalContainerEventFilterDelegate,
+                         internal::DisplayManagerDelegate,
                          public ui::EventTarget {
  public:
   typedef std::vector<aura::RootWindow*> RootWindowList;
@@ -441,6 +443,9 @@ class ASH_EXPORT Shell : internal::SystemModalContainerEventFilterDelegate,
   virtual EventTarget* GetParentTarget() OVERRIDE;
   virtual void OnEvent(ui::Event* event) OVERRIDE;
 
+  // ash::internal::DisplayManagerDelegate overrides:
+  virtual aura::RootWindowDelegate* CreateRootWindowDelegate() OVERRIDE;
+
   static Shell* instance_;
 
   // If set before the Shell is initialized, the mouse cursor will be hidden