dart:js_util - fix spelling

sdk/lib/js_util/dart2js/js_util_dart2js.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// Utility methods to efficiently manipulate typed JSInterop objects in cases
 /// where the name to call is not known at runtime. You should only use these
 /// methods when the same effect cannot be achieved with @JS annotations.
 /// These methods would be extension methods on JSObject if Dart supported
 /// extension methods.
 library dart.js_util;
 
 import 'dart:_foreign_helper' show JS;
 import 'dart:collection' show HashMap;
 
-/// WARNING: performance of this method is much worse than other uitil
+/// WARNING: performance of this method is much worse than other util
 /// methods in this library. Only use this method as a last resort.
 ///
 /// Recursively converts a JSON-like collection of Dart objects to a
 /// collection of JavaScript objects and returns a [JsObject] proxy to it.
 ///
 /// [object] must be a [Map] or [Iterable], the contents of which are also
 /// converted. Maps and Iterables are copied to a new JavaScript object.
-/// Primitives and other transferrable values are directly converted to their
+/// Primitives and other transferable values are directly converted to their
 /// JavaScript type, and all other objects are proxied.
 jsify(object) {
   if ((object is! Map) && (object is! Iterable)) {
     throw new ArgumentError("object must be a Map or Iterable");
   }
   return _convertDataTree(object);
 }
 
 _convertDataTree(data) {
   var _convertedObjects = new HashMap.identity();
@@ skipping 83 matching lines @@
   // object for which there is an interceptor
   return JS('Object', 'new #()', factoryFunction);
 
   // TODO(sra): Investigate:
   //
   //     var jsObj = JS('', 'Object.create(#.prototype)', constr);
   //     JS('', '#.apply(#, #)', constr, jsObj,
   //         []..addAll(arguments.map(_convertToJS)));
   //     return _wrapToDart(jsObj);
 }