CPP bindings: DCHECK when a Callback is destructed without being invoked

mojo/public/tools/bindings/generators/cpp_templates/interface_stub_declaration.tmpl

Index: mojo/public/tools/bindings/generators/cpp_templates/interface_stub_declaration.tmpl
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/interface_stub_declaration.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/interface_stub_declaration.tmpl
index afc6504dc81f33bf535546964eafcd06a29d266b..d9bbd75e5081cf76db35b3136a0dd7eea0bfd609 100644
--- a/mojo/public/tools/bindings/generators/cpp_templates/interface_stub_declaration.tmpl
+++ b/mojo/public/tools/bindings/generators/cpp_templates/interface_stub_declaration.tmpl
@@ -8,6 +8,25 @@ class {{interface.name}}Stub : public mojo::MessageReceiverWithResponder {
   virtual bool AcceptWithResponder(mojo::Message* message,
                                    mojo::MessageReceiver* responder) override;
 
+  void OnConnectionError() {
+    connection_error_occurred_ = true;
+  }
+  
+  bool connection_error_occurred() const {
+    return connection_error_occurred_;
+  }
+  
+  void Close() {
+    closed_ = true;
+  }
+  
+  bool closed() {
+    return closed_;
+  }
+  
+  
  private:
   {{interface.name}}* sink_;
+  bool connection_error_occurred_;
+  bool closed_;
 };