Refactor stateful parts of Component into StatefulComponent

sky/sdk/lib/editing/input.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 '../painting/text_style.dart';
 import '../widgets/basic.dart';
 import '../widgets/theme.dart';
 import 'editable_string.dart';
 import 'editable_text.dart';
 import 'keyboard.dart';
 
 typedef void ValueChanged(value);
 
 const double _kHintOpacity = 0.26;
 const EdgeDims _kTextfieldPadding = const EdgeDims.symmetric(vertical: 8.0);
 
-class Input extends Component {
+class Input extends StatefulComponent {
 
   Input({String key,
          this.placeholder,
          this.onChanged,
          this.focused})
-      : super(key: key, stateful: true) {
+      : super(key: key) {
     _editableValue = new EditableString(
       text: _value,
       onUpdated: _handleTextUpdated
     );
   }
 
   String placeholder;
   ValueChanged onChanged;
   bool focused = false;
 
@@ skipping 65 matching lines @@
       onPointerDown: (_) => keyboard.showByRequest()
     );
   }
 
   void didUnmount() {
     if (_isAttachedToKeyboard)
       keyboard.hide();
     super.didUnmount();
   }
 }