Convert legacy 'native code' to JS-forms in dart:html

lib/html/src/dart2js_FactoryProviders.dart

 // Copyright (c) 2012, 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.
 
 class _AudioContextFactoryProvider {
 
-  static AudioContext createAudioContext() native '''
-    var constructor = window.AudioContext || window.webkitAudioContext;
-    return new constructor();
-''';
+  static AudioContext createAudioContext() {
+    return JS('AudioContext',
+              'new (window.AudioContext || window.webkitAudioContext)()');
+  }
 }
 
 class _PointFactoryProvider {
-  static Point createPoint(num x, num y) native
-    'return new WebKitPoint(x, y);';
+  static Point createPoint(num x, num y) =>
+      JS('Point', 'new WebKitPoint(#, #)', x, y);
 }
 
 class _WebSocketFactoryProvider {
-  static WebSocket createWebSocket(String url) native
-      '''return new WebSocket(url);''';
+  static WebSocket createWebSocket(String url) =>
+      JS('WebSocket', 'new WebSocket(#)', url);
 }
 
 class _TextFactoryProvider {
-  static Text createText(String data) native
-      "return document.createTextNode(data);";
+  static Text createText(String data) =>
+      JS('Text', 'document.createTextNode(#)', data);
 }