Support custom to native conversions.

lib/dom/templates/dom/native/cpp_header.template

Index: lib/dom/templates/dom/native/cpp_header.template
diff --git a/lib/dom/templates/dom/native/cpp_header.template b/lib/dom/templates/dom/native/cpp_header.template
index 315588a25f72b79d3d04a443cb9d4861034d2dcc..31000c9fafc4fc6b8f04883aae61dbf50e6a366d 100644
--- a/lib/dom/templates/dom/native/cpp_header.template
+++ b/lib/dom/templates/dom/native/cpp_header.template
@@ -18,15 +18,11 @@ struct Dart$INTERFACE {
     typedef $WEBCORE_CLASS_NAME NativeType;
     typedef $NATIVE_TRAITS_TYPE NativeTraits;
 
-    static PassRefPtr<NativeType> toNative(Dart_Handle handle, Dart_Handle& exception)
-    {
-        return DartDOMWrapper::unwrapDartWrapper<Dart$INTERFACE>(handle, exception);
-    }
-
+$TO_NATIVE
     static Dart_NativeFunction resolver(Dart_Handle name, int argumentCount);
 };
 
-$TO_DART_VALUE
+$TO_DART
 inline Dart_Handle toDartValue(PassRefPtr< $WEBCORE_CLASS_NAME > value)
 {
     return toDartValue(value.get());