aura-mus: add a drag representation image.

mash/simple_wm/simple_wm.cc

Index: mash/simple_wm/simple_wm.cc
diff --git a/mash/simple_wm/simple_wm.cc b/mash/simple_wm/simple_wm.cc
index f4633121ba0858185a94129c06a096ea3a9946d2..4d75e064e9ffc3e689048ff10bd3452e537f516a 100644
--- a/mash/simple_wm/simple_wm.cc
+++ b/mash/simple_wm/simple_wm.cc
@@ -464,6 +464,15 @@ void SimpleWM::OnWmClientJankinessChanged(
   // Don't care.
 }
 
+void SimpleWM::OnWmBuildDragImage(const gfx::Point& cursor_location,
+                                  const SkBitmap& drag_image,
+                                  const gfx::Vector2d& drag_image_offset,
+                                  ui::mojom::DragEventSource source) {}
+
+void SimpleWM::OnWmMoveDragImage(const gfx::Point& cursor_location) {}
+
+void SimpleWM::OnWmDestroyDragImage() {}
+
 void SimpleWM::OnWmWillCreateDisplay(const display::Display& display) {
   screen_->display_list().AddDisplay(display,
                                      display::DisplayList::Type::PRIMARY);