Fix issues that broke editing on browsers without Shadow DOM support.

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.
 
 library trydart.paste_test;
 
 import 'dart:html';
 import 'dart:async';
 
 import 'package:try/src/interaction_manager.dart' show
@@ skipping 28 matching lines @@
 
 Future runTests() {
   Iterator<String> keys = tests.keys.iterator;
   keys.moveNext();
   mainEditorPane.innerHtml = keys.current;
 
   Future makeFuture() => new Future(() {
     String key = keys.current;
     print('Checking $key');
     queryDiagnosticNodes().forEach((Node node) {
-      node.parent.insertBefore(
-          new Text('<DIAGNOSTIC>'), node.parent.firstChild);
-      node.replaceWith(new Text('</DIAGNOSTIC>'));
+      node.parent.append(new Text('</DIAGNOSTIC>'));
+      node.replaceWith(new Text('<DIAGNOSTIC>'));

[ahe, 2014/07/04 13:52:00]

This code replaces diagnostics with <DIAGNOSTIC>...</DIAGNOSTIC>.

Before it was operating on:

<a>...<span>tip</span></a>

Now it looks like:

<a><span>tip</span>...</a>

       observer.takeRecords(); // Discard mutations.
     });
     Expect.stringEquals(tests[key], mainEditorPane.text);
     if (keys.moveNext()) {
       key = keys.current;
       print('Setting $key');
       mainEditorPane.innerHtml = key;
       return makeFuture();
     } else {
       // Clear the DOM to work around a bug in test.dart.
@@ skipping 10 matching lines @@
 
   var interaction = new InteractionManager();
   mainEditorPane = new DivElement();
   document.body.append(mainEditorPane);
   observer = new MutationObserver(interaction.onMutation)
       ..observe(
           mainEditorPane, childList: true, characterData: true, subtree: true);
 
   asyncTest(runTests);
 }