aura-mus: add a drag representation image.

services/ui/demo/mus_demo_internal.h

Index: services/ui/demo/mus_demo_internal.h
diff --git a/services/ui/demo/mus_demo_internal.h b/services/ui/demo/mus_demo_internal.h
index f79da0de2a9a09094d00fef5c3c2e77499e40e00..7c86b3a93eac307a5e85133e7c54ff8c97de2a01 100644
--- a/services/ui/demo/mus_demo_internal.h
+++ b/services/ui/demo/mus_demo_internal.h
@@ -43,6 +43,12 @@ class MusDemoInternal : public MusDemo, public aura::WindowManagerDelegate {
       std::map<std::string, std::vector<uint8_t>>* properties) final;
   void OnWmClientJankinessChanged(const std::set<aura::Window*>& client_windows,
                                   bool janky) final;
+  void OnWmBuildDragImage(const gfx::Point& screen_location,
+                          const SkBitmap& drag_image,
+                          const gfx::Vector2d& drag_image_offset,
+                          ui::mojom::PointerKind source) final;
+  void OnWmMoveDragImage(const gfx::Point& screen_location) final;
+  void OnWmDestroyDragImage() final;
   void OnWmWillCreateDisplay(const display::Display& display) final;
   void OnWmNewDisplay(std::unique_ptr<aura::WindowTreeHostMus> window_tree_host,
                       const display::Display& display) final;