Mojo C++ bindings: more consistent Clone() and Equals().

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

 {% from "enum_macros.tmpl" import enum_decl -%}
 
 class {{struct.name}} {
  public:
   using Data_ = internal::{{struct.name}}_Data;
 
 {#--- Enums #}
 {%- for enum in struct.enums -%}
   {{enum_decl(enum)|indent(2)}}
 {%- endfor %}
@@ skipping 16 matching lines @@
 
   template <typename U>
   U To() const {
     return mojo::TypeConverter<U, {{struct.name}}>::Convert(*this);
   }
 
   {{struct.name}}();
   ~{{struct.name}}();
 
   // Clone() is a template so it is only instantiated if it is used. Thus, the
-  // bindings generator does not need to know whether typemapped native types
-  // support operator=.
+  // bindings generator does not need to know whether Clone() or copy
+  // constructor/assignment are available for members.
   template <typename StructPtrType = {{struct.name}}Ptr>
-  {{struct.name}}Ptr Clone() const {
-    // Use StructPtrType to prevent the compiler from trying to compile this
-    // without being asked.
-    StructPtrType rv(New());
-{%-   for field in struct.fields %}
-{%-     if field.kind|is_object_kind and not field.kind|is_string_kind and
-            not field.kind|is_typemapped_kind %}
-    rv->{{field.name}} = {{field.name}}.Clone();
-{%-     else %}
-    rv->{{field.name}} = {{field.name}};
-{%-     endif %}
-{%-   endfor %}
-    return rv;
-  }
+  {{struct.name}}Ptr Clone() const;
 
   // Equals() is a template so it is only instantiated if it is used. Thus, the
-  // bindings generator does not need to know whether typemapped native types
-  // support operator==.
+  // bindings generator does not need to know whether Equals() or == operator
+  // are available for members.
   template <typename T,
             typename std::enable_if<std::is_same<
                 T, {{struct.name}}>::value>::type* = nullptr>
-  bool Equals(const T& other) const {
-  {%-  for field in struct.fields %}
-    if (!mojo::internal::ValueTraits<{{field.kind|cpp_wrapper_type}}>::Equals(this->{{field.name}}, other.{{field.name}}))
-      return false;
-  {%-  endfor %}
-    return true;
-  }
+  bool Equals(const T& other) const;
 
 {#--- Struct members #}
 {%  for field in struct.fields %}
 {%-   set type = field.kind|cpp_wrapper_type %}
 {%-   set name = field.name %}
   {{type}} {{name}};
 {%- endfor %}
 };