Make Mandoline shut down cleanly.

components/window_manager/window_manager_app.h

Index: components/window_manager/window_manager_app.h
diff --git a/components/window_manager/window_manager_app.h b/components/window_manager/window_manager_app.h
index 81a2e4633b3ef703d1a12116f33a41f06a8d5607..89a9b35094e118edadb1793c9eecf3945de99fa9 100644
--- a/components/window_manager/window_manager_app.h
+++ b/components/window_manager/window_manager_app.h
@@ -45,7 +45,8 @@ class WindowManagerApp
       public mojo::ViewObserver,
       public mojo::InterfaceFactory<mojo::WindowManager>,
       public mojo::InterfaceFactory<mojo::WindowManagerInternal>,
-      public mojo::WindowManagerInternal {
+      public mojo::WindowManagerInternal,
+      public mojo::ErrorHandler {
  public:
   WindowManagerApp(ViewManagerDelegate* view_manager_delegate,
                    WindowManagerDelegate* window_manager_delegate);
@@ -113,6 +114,9 @@ class WindowManagerApp
       mojo::ScopedMessagePipeHandle view_manager_client_request) override;
   void OnAccelerator(mojo::EventPtr event) override;
 
+  // ErrorHandler:
+  void OnConnectionError() override;
+
   mojo::Shell* shell_;
 
   ViewManagerDelegate* wrapped_view_manager_delegate_;