Fixs bug in notifying clients about hierarchy changes

services/ui/public/cpp/window_tree_client.h

Index: services/ui/public/cpp/window_tree_client.h
diff --git a/services/ui/public/cpp/window_tree_client.h b/services/ui/public/cpp/window_tree_client.h
index 9d993fad78395de4d2b54eadc9111f4869049513..0a942c2187cf46621dae4b6db93fec255a592c04 100644
--- a/services/ui/public/cpp/window_tree_client.h
+++ b/services/ui/public/cpp/window_tree_client.h
@@ -250,8 +250,8 @@ class WindowTreeClient : public mojom::WindowTreeClient,
 
   static Id server_id(const Window* window) { return window->server_id(); }
 
-  Window* BuildWindowTree(const mojo::Array<mojom::WindowDataPtr>& windows,
-                          Window* initial_parent);
+  void BuildWindowTree(const mojo::Array<mojom::WindowDataPtr>& windows,
+                       Window* initial_parent);
 
   Window* NewWindowImpl(NewWindowType type,
                         const Window::SharedProperties* properties);