Move DisplayManager and DisplayChangeObserverX11 from aura to ash.

ui/gfx/screen_gtk.cc

Index: ui/gfx/screen_gtk.cc
diff --git a/ui/gfx/screen_gtk.cc b/ui/gfx/screen_gtk.cc
index 5aefb15400141411b3e66a6a21657df994684fca..8ef803dca1f3e4de57cc39ac80d0de454a6dae96 100644
--- a/ui/gfx/screen_gtk.cc
+++ b/ui/gfx/screen_gtk.cc
@@ -165,6 +165,14 @@ class ScreenGtk : public gfx::Screen {
     return display;
   }
 
+  virtual void AddObserver(gfx::DisplayObserver* observer) OVERRIDE {
+    // TODO(oshima): crbug.com/122863.
+  }
+
+  virtual void RemoveObserver(gfx::DisplayObserver* observer) OVERRIDE {
+    // TODO(oshima): crbug.com/122863.
+  }
+
  private:
   DISALLOW_COPY_AND_ASSIGN(ScreenGtk);
 };