Added link to HTML5 samples to the top of HTML library.

tools/dom/templates/html/dart2js/html_dart2js.darttemplate

 // 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.
 
 // DO NOT EDIT - unless you are editing documentation as per:
 // https://code.google.com/p/dart/wiki/ContributingHTMLDocumentation
 // Auto-generated dart:html library.
 
 /// The Dart HTML library.
+///
+/// For examples, see [Dart HTML5 Samples](https://github.com/dart-lang/dart-html5-samples) on Github.
 library dart.dom.html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev' hide Symbol;
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
 import 'dart:json' as json;
 import 'dart:math';
@@ skipping 66 matching lines @@
   return JS('int', r'window.$dart$isolate$counter++');
 }
 
 // Fast path to invoke JS send port.
 _callPortSync(int id, message) {
   return JS('var', r'ReceivePortSync.dispatchCall(#, #)', id, message);
 }
 
 Future<SendPort> spawnDomFunction(Function f) =>
   new Future.value(IsolateNatives.spawnDomFunction(f));