ash: Add RootWindowHostFactory class.

ash/display/display_manager.h

Index: ash/display/display_manager.h
diff --git a/ash/display/display_manager.h b/ash/display/display_manager.h
index 292da15f898c56cde0745166b1aa001a83f3c70d..5292d36691d3720d20ff4e61ced988170119de0b 100644
--- a/ash/display/display_manager.h
+++ b/ash/display/display_manager.h
@@ -27,6 +27,7 @@ class DisplayManagerTestApi;
 class SystemGestureEventFilterTest;
 }
 namespace internal {
+class DisplayManagerDelegate;
 
 // DisplayManager maintains the current display configurations,
 // and notifies observers when configuration changes.
@@ -36,7 +37,7 @@ namespace internal {
 // if the root window is translated. crbug.com/119268.
 class ASH_EXPORT DisplayManager : public aura::RootWindowObserver {
  public:
-  DisplayManager();
+  DisplayManager(DisplayManagerDelegate* delegate);
   virtual ~DisplayManager();
 
   // Used to emulate display change when run in a desktop environment instead
@@ -183,6 +184,8 @@ class ASH_EXPORT DisplayManager : public aura::RootWindowObserver {
   // The mapping from the display ID to its internal data.
   std::map<int64, DisplayInfo> display_info_;
 
+  DisplayManagerDelegate* delegate_;
+
   DISALLOW_COPY_AND_ASSIGN(DisplayManager);
 };