Move DisplayManager and DisplayChangeObserverX11 from aura to ash.

ui/gfx/screen.h

Index: ui/gfx/screen.h
diff --git a/ui/gfx/screen.h b/ui/gfx/screen.h
index 1a04214395283a286e4fc9fd06ca5990f5fd949e..9410d028889bb4cadaafa37039159030171acc17 100644
--- a/ui/gfx/screen.h
+++ b/ui/gfx/screen.h
@@ -13,6 +13,7 @@
 #include "ui/gfx/screen_type_delegate.h"
 
 namespace gfx {
+class DisplayObserver;
 class Rect;
 
 // A utility class for getting various info about screen size, displays,
@@ -70,6 +71,10 @@ class UI_EXPORT Screen {
   // Returns the primary display.
   virtual gfx::Display GetPrimaryDisplay() const = 0;
 
+  // Adds/Removes display observers.
+  virtual void AddObserver(DisplayObserver* observer) = 0;
+  virtual void RemoveObserver(DisplayObserver* observer) = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(Screen);
 };