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

services/ui/ws/test_utils.cc

Index: services/ui/ws/test_utils.cc
diff --git a/services/ui/ws/test_utils.cc b/services/ui/ws/test_utils.cc
index e60c7c1595343402944ab6ff1826511f5e82dae7..04fe6d6472a5893630bfee55187f89838f25a9b9 100644
--- a/services/ui/ws/test_utils.cc
+++ b/services/ui/ws/test_utils.cc
@@ -381,6 +381,9 @@ void TestWindowTreeClient::OnCompleteDrop(
     uint32_t effect_bitmask,
     const OnCompleteDropCallback& callback) {}
 
+void TestWindowTreeClient::OnDragCompletedReturnValue(uint32_t window,
+                                                      uint32_t action_taken) {}
+
 void TestWindowTreeClient::OnDragDropDone() {}
 
 void TestWindowTreeClient::OnChangeCompleted(uint32_t change_id, bool success) {