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

sky/engine/tonic/dart_wrappable.cc

Index: sky/engine/tonic/dart_wrappable.cc
diff --git a/sky/engine/tonic/dart_wrappable.cc b/sky/engine/tonic/dart_wrappable.cc
index 6c7e3a15267fff3b4a7c22cbbdb5dafe79cffc24..1bf69d4cf5b023ba6101340539b1f5c3b40edcde 100644
--- a/sky/engine/tonic/dart_wrappable.cc
+++ b/sky/engine/tonic/dart_wrappable.cc
@@ -50,9 +50,9 @@ void DartWrappable::FinalizeDartWrapper(void* isolate_callback_data,
 }
 
 DartWrappable* DartConverterWrappable::FromDart(Dart_Handle handle) {
-  intptr_t* peer = 0;
+  intptr_t peer = 0;
   Dart_Handle result =
-      Dart_GetNativeInstanceField(handle, DartWrappable::kPeerIndex, peer);
+      Dart_GetNativeInstanceField(handle, DartWrappable::kPeerIndex, &peer);
   if (Dart_IsError(result))
     return nullptr;
   return reinterpret_cast<DartWrappable*>(peer);