Hide internal methods like wrap_jso from the dart:html public interface

sdk/lib/html/html_common/conversions_dart2js.dart

 part of html_common;
 
 /// Converts a JavaScript object with properties into a Dart Map.
 /// Not suitable for nested objects.
 Map convertNativeToDart_Dictionary(object) {
   if (object == null) return null;
   var dict = {};
   var keys = JS('JSExtendableArray', 'Object.getOwnPropertyNames(#)', object);
   for (final key in keys) {
     dict[key] = JS('var', '#[#]', object, key);
@@ skipping 73 matching lines @@
 bool isJavaScriptPromise(value) =>
     JS('bool', r'typeof Promise != "undefined" && # instanceof Promise', value);
 
 Future convertNativePromiseToDartFuture(promise) {
   var completer = new Completer();
   var then = convertDartClosureToJS((result) => completer.complete(result), 1);
   var error = convertDartClosureToJS((result) => completer.completeError(result), 1);
   var newPromise = JS('', '#.then(#).catch(#)', promise, then, error);
   return completer.future;
 }
+
+/// Wrap a JS object with an instance of the matching dart:html class. Used only in Dartium.
+wrap_jso(jsObject) => jsObject;
+
+/// Find the underlying JS object for a dart:html Dart object.
+unwrap_jso(dartClass_instance) => dartClass_instance;