Mojo C++ bindings: introduce an optional array to store transferred interface IDs in messages.

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

 {%- import "interface_macros.tmpl" as interface_macros %}
 class {{export_attribute}} {{interface.name}}Proxy
     : public {{interface.name}} {
  public:
   explicit {{interface.name}}Proxy(mojo::MessageReceiverWithResponder* receiver);
 
 {%- for method in interface.methods %}
 {%-   if method.sync %}
   bool {{method.name}}({{interface_macros.declare_sync_method_params("", method)}}) override;
 {%-   endif %}
   void {{method.name}}({{interface_macros.declare_request_params("", method, use_once_callback)}}) override;
 {%- endfor %}
 
-  void set_group_controller(
-        scoped_refptr<mojo::AssociatedGroupController> group_controller) {
-    group_controller_ = std::move(group_controller);
-  }
  private:
   mojo::MessageReceiverWithResponder* receiver_;
-  scoped_refptr<mojo::AssociatedGroupController> group_controller_;
 };