Random fixes for mash bridge classes

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_