Mojo: Replace RemotePtr with InterfacePtr and InterfaceImpl

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

 class {{interface.name}}Stub : public mojo::MessageReceiver {
  public:
-  explicit {{interface.name}}Stub({{interface.name}}* sink);
+  {{interface.name}}Stub();
+  void set_sink({{interface.name}}* sink) { sink_ = sink; }
+  {{interface.name}}* sink() { return sink_; }
 
   virtual bool Accept(mojo::Message* message) MOJO_OVERRIDE;
   virtual bool AcceptWithResponder(mojo::Message* message,
                                    mojo::MessageReceiver* responder)
                                        MOJO_OVERRIDE;
 
  private:
   {{interface.name}}* sink_;
 };