Random fixes for mash bridge classes

components/mus/public/cpp/window_tree_connection_observer.h

Index: components/mus/public/cpp/window_tree_connection_observer.h
diff --git a/components/mus/public/cpp/window_tree_connection_observer.h b/components/mus/public/cpp/window_tree_connection_observer.h
index b29d71cd711d111cfb9239ef774d59242fcf769e..8577cae5ad7737c770e3b3871fed81f615e99c03 100644
--- a/components/mus/public/cpp/window_tree_connection_observer.h
+++ b/components/mus/public/cpp/window_tree_connection_observer.h
@@ -8,12 +8,16 @@
 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() {}
 };