Relocate display_manager from ash to ui

ash/display/screen_ash.h

Index: ash/display/screen_ash.h
diff --git a/ash/display/screen_ash.h b/ash/display/screen_ash.h
index 15337a2d988933d709b5398e1b7104c46f06e8bb..c315caf77a55ab31ecd022241bed6c470d38c99f 100644
--- a/ash/display/screen_ash.h
+++ b/ash/display/screen_ash.h
@@ -12,6 +12,7 @@
 #include "ui/display/screen.h"
 
 namespace display {
+class DisplayManager;
 class DisplayObserver;
 }
 
@@ -20,7 +21,6 @@ class Rect;
 }
 
 namespace ash {
-class DisplayManager;
 
 // Aura implementation of display::Screen. Implemented here to avoid circular
 // dependencies.
@@ -45,7 +45,7 @@ class ASH_EXPORT ScreenAsh : public display::Screen {
   void RemoveObserver(display::DisplayObserver* observer) override;
 
   // CreateDisplayManager with a ScreenAsh instance.
-  static DisplayManager* CreateDisplayManager();
+  static display::DisplayManager* CreateDisplayManager();
 
   // Create a screen instance to be used during shutdown.
   static void CreateScreenForShutdown();