Eliminate WindowTreeConnection

components/mus/public/cpp/window_tree_connection_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_CONNECTION_OBSERVER_H_
-#define COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CONNECTION_OBSERVER_H_
-
-namespace mus {
-
-class Window;
-class WindowTreeConnection;
-
-class WindowTreeConnectionObserver {
- public:
-  virtual void OnWindowTreeFocusChanged(Window* gained_focus,
-                                        Window* lost_focus) {}
-
-  // Called right before the connection is destroyed.
-  virtual void OnWillDestroyConnection(WindowTreeConnection* connection) {}
-
- protected:
-  virtual ~WindowTreeConnectionObserver() {}
-};
-
-}  // namespace mus
-
-#endif  // COMPONENTS_MUS_PUBLIC_CPP_WINDOW_TREE_CONNECTION_OBSERVER_H_