Morph the APIs for Node, ParentNode, and Element closer to the specs

sky/engine/tonic/dart_wrappable.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SKY_ENGINE_TONIC_DART_WRAPPABLE_H_
 #define SKY_ENGINE_TONIC_DART_WRAPPABLE_H_
 
 #include "base/logging.h"
 #include "base/template_util.h"
 #include "dart/runtime/include/dart_api.h"
@@ skipping 108 matching lines @@
     return static_cast<T*>(DartConverterWrappable::FromArgumentsWithNullCheck(
         args, index, exception));
   }
 };
 
 template<typename T>
 struct DartConverter<RefPtr<T>> {
   static Dart_Handle ToDart(RefPtr<T> val) {
     return DartConverter<T*>::ToDart(val.get());
   }
+
+  static RefPtr<T> FromDart(Dart_Handle handle) {
+    return DartConverter<T*>::FromDart(handle);
+  }
 };
 
 template<typename T>
 static T* GetReceiver(Dart_NativeArguments args) {
   intptr_t receiver;
   Dart_Handle result = Dart_GetNativeReceiver(args, &receiver);
   DCHECK(!Dart_IsError(result));
   return static_cast<T*>(reinterpret_cast<DartWrappable*>(receiver));
 }
 
 }  // namespace blink
 
 #endif  // SKY_ENGINE_TONIC_DART_WRAPPABLE_H_