Eliminate WindowTreeConnection

components/mus/public/cpp/window_tree_client_observer.h

+// Copyright 2015 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 COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CLIENT_OBSERVER_H_
+#define COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CLIENT_OBSERVER_H_
+
+namespace mus {
+
+class Window;
+class WindowTreeClient;
+
+class WindowTreeClientObserver {
+ public:
+  virtual void OnWindowTreeFocusChanged(Window* gained_focus,
+                                        Window* lost_focus) {}
+
+  // Called right before the client is destroyed.
+  virtual void OnWillDestroyClient(WindowTreeClient* client) {}
+
+ protected:
+  virtual ~WindowTreeClientObserver() {}
+};
+
+}  // namespace mus
+
+#endif  // COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CLIENT_OBSERVER_H_