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

ui/aura/test/test_window_delegate.cc

Index: ui/aura/test/test_window_delegate.cc
diff --git a/ui/aura/test/test_window_delegate.cc b/ui/aura/test/test_window_delegate.cc
index e5ae364b5fd28e7c8aeb460c6fa8ca9e5cec3093..96aa57fd32140afb8cb9888f592ac4c3c1819087 100644
--- a/ui/aura/test/test_window_delegate.cc
+++ b/ui/aura/test/test_window_delegate.cc
@@ -50,10 +50,6 @@ void TestWindowDelegate::OnBoundsChanged(const gfx::Rect& old_bounds,
                                          const gfx::Rect& new_bounds) {
 }
 
-gfx::NativeCursor TestWindowDelegate::GetCursor(const gfx::Point& point) {
-  return gfx::kNullCursor;
-}
-
 int TestWindowDelegate::GetNonClientComponent(const gfx::Point& point) const {
   return window_component_;
 }