mus drag and drop: return the completed effect to the caller.

services/ui/ws/test_utils.h

Index: services/ui/ws/test_utils.h
diff --git a/services/ui/ws/test_utils.h b/services/ui/ws/test_utils.h
index 899b35d41e6eb15536e02a5ff32e97e2f3f4e8dd..f1cf568bc7fa337b85874e9a5d54ac1ebd73ae92 100644
--- a/services/ui/ws/test_utils.h
+++ b/services/ui/ws/test_utils.h
@@ -456,6 +456,9 @@ class TestWindowTreeClient : public ui::mojom::WindowTreeClient {
                       const gfx::Point& position,
                       uint32_t effect_bitmask,
                       const OnCompleteDropCallback& callback) override;
+  void OnPerformDragDropCompleted(uint32_t window,
+                                  bool success,
+                                  uint32_t action_taken) override;
   void OnDragDropDone() override;
   void OnChangeCompleted(uint32_t change_id, bool success) override;
   void RequestClose(uint32_t window_id) override;