aura-mus: add a drag representation image.

mash/simple_wm/simple_wm.h

Index: mash/simple_wm/simple_wm.h
diff --git a/mash/simple_wm/simple_wm.h b/mash/simple_wm/simple_wm.h
index 2d4e283e5ccce90a26ea3b455f1277f4659770fb..cf85c861f78202b7409b03a52480bca8f9bf6a35 100644
--- a/mash/simple_wm/simple_wm.h
+++ b/mash/simple_wm/simple_wm.h
@@ -83,6 +83,12 @@ class SimpleWM : public service_manager::Service,
       std::map<std::string, std::vector<uint8_t>>* properties) override;
   void OnWmClientJankinessChanged(const std::set<aura::Window*>& client_windows,
                                   bool janky) override;
+  void OnWmBuildDragImage(const gfx::Point& screen_location,
+                          const SkBitmap& drag_image,
+                          const gfx::Vector2d& drag_image_offset,
+                          ui::mojom::PointerKind source) override;
+  void OnWmMoveDragImage(const gfx::Point& screen_location) override;
+  void OnWmDestroyDragImage() override;
   void OnWmWillCreateDisplay(const display::Display& display) override;
   void OnWmNewDisplay(std::unique_ptr<aura::WindowTreeHostMus> window_tree_host,
                       const display::Display& display) override;