mus: Implement interwindow drag and drop

services/ui/ws/current_drag_operation_delegate.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SERVICES_UI_WS_CURRENT_DRAG_OPERATION_DELEGATE_H_
+#define SERVICES_UI_WS_CURRENT_DRAG_OPERATION_DELEGATE_H_
+
+namespace ui {
+namespace ws {
+
+class CurrentDragOperationDelegate {
+ public:
+  virtual ~CurrentDragOperationDelegate() {}
+
+  // Called when a drag operation is completed
+  virtual void OnDragOver(bool success) = 0;
+};
+
+}  // namespace ws
+}  // namespace ui
+
+#endif  // SERVICES_UI_WS_CURRENT_DRAG_OPERATION_DELEGATE_H_