Mojo: Simplify object serialization

mojo/public/bindings/generators/cpp_templates/params_definition.tmpl

 {%- import "struct_macros.tmpl" as struct_macros %}
 {%- set class_name = struct.name ~ "_Data" %}
 {%- set method_name = "k%s_%s_Name"|format(interface.name, method.name) %}
 const uint32_t {{method_name}} = {{method.ordinal}};
 class {{class_name}} {
  public:
   static {{class_name}}* New(mojo::Buffer* buf) {
     return new (buf->Allocate(sizeof({{class_name}})))
         {{class_name}}();
   }
 
 {#--- Setters -#}
 {{ struct_macros.setters(struct) }}
 
 {#--- Getters -#}
 {{ struct_macros.getters(struct) }}
 
+  void CloseHandles() {
+{%- for pf in struct.packed.packed_fields if pf.field.kind|is_object_kind %}
+    if ({{pf.field.name}}_.ptr)
+      {{pf.field.name}}_.ptr->CloseHandles();
+{%- endfor %}
+  }
+
+  void EncodePointersAndHandles(std::vector<mojo::Handle>* handles) {
+    {{ struct_macros.encodes(struct)|indent(4) }}
+  }
+
+  bool DecodePointersAndHandles(mojo::Message* message) {
+    {{ struct_macros.decodes(struct)|indent(4) }}
+    return true;
+  }
+
  private:
-  friend class mojo::internal::ObjectTraits<{{class_name}}>;
-
   {{class_name}}() {
     _header_.num_bytes = sizeof(*this);
     _header_.num_fields = 3;
   }
 
   mojo::internal::StructHeader _header_;
 {{ struct_macros.fields(struct) }}
 };
 MOJO_COMPILE_ASSERT(sizeof({{class_name}}) == {{struct.packed|struct_size}},
                     bad_sizeof_{{class_name}});