aura-mus: add a drag representation image.

services/ui/demo/mus_demo_internal.cc

Index: services/ui/demo/mus_demo_internal.cc
diff --git a/services/ui/demo/mus_demo_internal.cc b/services/ui/demo/mus_demo_internal.cc
index 8cbabf750eaf4548e951414fee7970841622660a..19a63f0a435fe6665c2907093f6ab01f89db4ae7 100644
--- a/services/ui/demo/mus_demo_internal.cc
+++ b/services/ui/demo/mus_demo_internal.cc
@@ -65,6 +65,15 @@ void MusDemoInternal::OnWmClientJankinessChanged(
   // Don't care
 }
 
+void MusDemoInternal::OnWmBuildDragImage(const gfx::Point& cursor_location,
+                                         const SkBitmap& drag_image,
+                                         const gfx::Vector2d& drag_image_offset,
+                                         ui::mojom::DragEventSource source) {}
+
+void MusDemoInternal::OnWmMoveDragImage(const gfx::Point& cursor_location) {}
+
+void MusDemoInternal::OnWmDestroyDragImage() {}
+
 void MusDemoInternal::OnWmWillCreateDisplay(const display::Display& display) {
   AddPrimaryDisplay(display);
 }