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

dart/tests/try/cursor_position_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.
 
 // Test that cursor positions are correctly updated after adding new content.
 
 import 'test_try.dart';
 
 void main() {
   InteractionManager interaction = mockTryDartInteraction();
@@ skipping 31 matching lines @@
 
     new TestCase('Test adding a new line with mock key event.', () {
       clearEditorPaneWithoutNotifications();
       checkSelectionIsCollapsed(mainEditorPane, 0);
       simulateEnterKeyDown(interaction);
     }, checkAtBeginningOfSecondLine),
 
     new TestCase('Clear and presetup the test', () {
       clearEditorPaneWithoutNotifications();
       mainEditorPane.text = 'var greeting = "Hello, World!\n";';
-    }, () { 
-      checkLineCount(2); 
+    }, () {
+      checkLineCount(2);
     }),
-    
+
     new TestCase('Test removing a split line', () {
       mainEditorPane.nodes.first.nodes.last.remove();
-    }, () { 
-      checkLineCount(1); 
+    }, () {
+      checkLineCount(1);
     }),
   ]);
 }
 
 void simulateEnterKeyDown(InteractionManager interaction) {
   interaction.onKeyUp(
       new MockKeyboardEvent('keydown', keyCode: KeyCode.ENTER));
 }
 
 void checkSelectionIsCollapsed(Node node, int offset) {
@@ skipping 35 matching lines @@
 
 class MockKeyboardEvent extends KeyEvent {
   final int keyCode;
 
   MockKeyboardEvent(String type, {int keyCode})
       : this.keyCode = keyCode,
         super.wrap(new KeyEvent(type, keyCode: keyCode));
 
   bool getModifierState(String keyArgument) => false;
 }