Move DisplayManager and DisplayChangeObserverX11 from aura to ash.

ui/gfx/screen_mac.mm

Index: ui/gfx/screen_mac.mm
diff --git a/ui/gfx/screen_mac.mm b/ui/gfx/screen_mac.mm
index 595ca3eb2d466bbfe107e0dc9174eab0042bd049..15bbf3728139395636176ee4b37f1c4afbf7baaa 100644
--- a/ui/gfx/screen_mac.mm
+++ b/ui/gfx/screen_mac.mm
@@ -168,6 +168,14 @@ class ScreenMac : 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(ScreenMac);
 };