aura-mus: add a drag representation image.

ui/aura/test/mus/test_window_tree.h

Index: ui/aura/test/mus/test_window_tree.h
diff --git a/ui/aura/test/mus/test_window_tree.h b/ui/aura/test/mus/test_window_tree.h
index 59d61178812dd9a6c52cbc0d73874edafb5da70c..872ae9410e7aae469ef31a00324ba44422d97974 100644
--- a/ui/aura/test/mus/test_window_tree.h
+++ b/ui/aura/test/mus/test_window_tree.h
@@ -193,8 +193,12 @@ class TestWindowTree : public ui::mojom::WindowTree {
   void PerformDragDrop(
       uint32_t change_id,
       uint32_t source_window_id,
+      const gfx::Point& screen_location,
       const std::unordered_map<std::string, std::vector<uint8_t>>& drag_data,
-      uint32_t drag_operation) override;
+      const SkBitmap& drag_image,
+      const gfx::Vector2d& drag_image_offset,
+      uint32_t drag_operation,
+      ui::mojom::DragEventSource source) override;
   void CancelDragDrop(uint32_t window_id) override;
   void PerformWindowMove(uint32_t change_id,
                          uint32_t window_id,