Refactor stateful parts of Component into StatefulComponent

sky/sdk/lib/editing/editable_text.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:async';
 import 'dart:sky' as sky;
 
 import '../painting/text_style.dart';
 import '../rendering/object.dart';
 import '../widgets/basic.dart';
 import 'editable_string.dart';
 
 const _kCursorBlinkPeriod = 500; // milliseconds
 const _kCursorGap = 1.0;
 const _kCursorHeightOffset = 2.0;
 const _kCursorWidth = 1.0;
 
-class EditableText extends Component {
+class EditableText extends StatefulComponent {
 
   EditableText({
     String key,
     this.value,
     this.focused: false,
     this.style,
-    this.cursorColor}) : super(key: key, stateful: true);
+    this.cursorColor}) : super(key: key);
 
   EditableString value;
   bool focused;
   TextStyle style;
   Color cursorColor;
 
   void syncFields(EditableText source) {
     value = source.value;
     focused = source.focused;
     style = source.style;
@@ skipping 64 matching lines @@
 
     Widget cursor = new Container(
       height: style.fontSize,
       width: _kCursorGap + _kCursorWidth,
       child: new CustomPaint(callback: _paintCursor, token: _showCursor)
     );
 
     return new Flex([text, cursor]);
   }
 }