mus: Keep track of the drag cursor during DnD operations.

services/ui/ws/drag_cursor_updater.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_DRAG_CURSOR_UPDATER_H_
+#define SERVICES_UI_WS_DRAG_CURSOR_UPDATER_H_
+
+namespace ui {
+namespace ws {
+
+// An interface for the DragController to signal that the cursor has changed.
+class DragCursorUpdater {
+ public:
+  virtual void OnDragCursorUpdated() = 0;
+
+ protected:
+  virtual ~DragCursorUpdater() {}
+};
+
+}  // namespace ws
+}  // namespace ui
+
+#endif  // SERVICES_UI_WS_DRAG_CURSOR_UPDATER_H_