Move GetCursor() method from WindowDelegate to its own delegate interface CursorDelegate.

ash/drag_drop/drag_drop_controller.cc

Index: ash/drag_drop/drag_drop_controller.cc
diff --git a/ash/drag_drop/drag_drop_controller.cc b/ash/drag_drop/drag_drop_controller.cc
index 4df5f713aa922d59ffabdb39cd2cda25745817bb..15429c80982d3289a851c29c08808292dd2609b8 100644
--- a/ash/drag_drop/drag_drop_controller.cc
+++ b/ash/drag_drop/drag_drop_controller.cc
@@ -95,9 +95,6 @@ class DragDropTrackerDelegate : public aura::WindowDelegate {
 
   virtual void OnBoundsChanged(const gfx::Rect& old_bounds,
                                const gfx::Rect& new_bounds) OVERRIDE {}
-  virtual gfx::NativeCursor GetCursor(const gfx::Point& point) OVERRIDE {
-    return gfx::kNullCursor;
-  }
   virtual int GetNonClientComponent(const gfx::Point& point) const OVERRIDE {
     return HTCAPTION;
   }