aura-mus: add a drag representation image.

services/ui/test_wm/test_wm.cc

Index: services/ui/test_wm/test_wm.cc
diff --git a/services/ui/test_wm/test_wm.cc b/services/ui/test_wm/test_wm.cc
index 25a369c7c5efd2e0107917e1972f50b4e3aa8ca5..991c50c16436e456420e2b069974f92801437b65 100644
--- a/services/ui/test_wm/test_wm.cc
+++ b/services/ui/test_wm/test_wm.cc
@@ -124,6 +124,12 @@ class TestWM : public service_manager::Service,
                                   bool janky) override {
     // Don't care.
   }
+  void OnWmBuildDragImage(const gfx::Point& cursor_location,
+                          const SkBitmap& drag_image,
+                          const gfx::Vector2d& drag_image_offset,
+                          ui::mojom::DragEventSource source) override {}
+  void OnWmMoveDragImage(const gfx::Point& cursor_location) override {}
+  void OnWmDestroyDragImage() override {}
   void OnWmWillCreateDisplay(const display::Display& display) override {
     // This class only deals with one display.
     DCHECK_EQ(0u, screen_->display_list().displays().size());