Mojo: Report bindings validation errors via MojoNotifyBadMessage

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

 class {{interface.name}}Stub : public mojo::MessageReceiverWithResponderStatus {
  public:
   {{interface.name}}Stub();
   ~{{interface.name}}Stub() override;
   void set_sink({{interface.name}}* sink) { sink_ = sink; }
   {{interface.name}}* sink() { return sink_; }
   mojo::internal::SerializationContext* serialization_context() {
     return &serialization_context_;
   }
 
-  bool Accept(mojo::Message* message) override;
-  bool AcceptWithResponder(mojo::Message* message,
+  Result Accept(mojo::Message* message) override;
+  Result AcceptWithResponder(
+      mojo::Message* message,
       mojo::MessageReceiverWithStatus* responder) override;
 
  private:
   {{interface.name}}* sink_;
   mojo::internal::SerializationContext serialization_context_;
   mojo::internal::ControlMessageHandler control_message_handler_;
 };