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

ash/display/cursor_window_controller.cc

Index: ash/display/cursor_window_controller.cc
diff --git a/ash/display/cursor_window_controller.cc b/ash/display/cursor_window_controller.cc
index 6fb1a08e84e7290ed73a1940d860b21bf3d1ca11..c4ee5b81942d110cad35d565303e39cd25982e18 100644
--- a/ash/display/cursor_window_controller.cc
+++ b/ash/display/cursor_window_controller.cc
@@ -34,9 +34,6 @@ class CursorWindowDelegate : public aura::WindowDelegate {
   virtual gfx::Size GetMaximumSize() const OVERRIDE { return size_; }
   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 HTNOWHERE;