Adding missing 'part of html' statements.

sdk/lib/html/src/dartium_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.
 
+part of html;
+
 class _AudioContextFactoryProvider {
   static AudioContext createAudioContext() => _createAudioContext();
   static _createAudioContext([int numberOfChannels,
                               int numberOfFrames,
                               int sampleRate])
       native "AudioContext_constructor_Callback";
 }
 
 class _IDBKeyRangeFactoryProvider {
 
@@ skipping 88 matching lines @@
 }
 
 class _WebSocketFactoryProvider {
   static WebSocket createWebSocket(String url) => _createWebSocket(url);
   static _createWebSocket(String url) native "WebSocket_constructor_Callback";
 }
 
 class _TextFactoryProvider {
   static Text createText(String data) => document.$dom_createTextNode(data);
 }