Simplify content rewriting.

dart/tests/try/paste_content_rewriting_test.dart

 // Copyright (c) 2014, 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.
 
 // SharedOptions=--package-root=sdk/lib/_internal/
 
 library trydart.paste_test;
 
 import 'dart:html';
 import 'dart:async';
@@ skipping 18 matching lines @@
   inputPre = new DivElement();
   document.body.append(inputPre);
   observer = new MutationObserver(interaction.onMutation)
       ..observe(inputPre, childList: true, characterData: true, subtree: true);
 
   inputPre.innerHtml = "<span><p>//...</p>}</span>";
 
   asyncTest(() => new Future(() {
     print('Welcome to the future');
     Expect.stringEquals('//...\n}\n', inputPre.text);
+  }).then((_) {
+    inputPre.innerHtml = 'someText';
+    return new Future(() {
+      Expect.stringEquals('someText\n', inputPre.text);
+
+      // Clear the DOM to work around a bug in test.dart.
+      document.body.nodes.clear();
+    });
   }));
 }