Begin work on the PopupMenu entrance animation

sky/framework/components/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 '../editing/editable_string.dart';
 import '../editing/editable_text.dart';
 import '../editing/keyboard.dart';
 import '../fn.dart';
 import '../theme/colors.dart';
 
@@ skipping 34 matching lines @@
   Input({Object key,
          this.placeholder,
          this.onChanged,
          this.focused})
       : super(key: key, stateful: true) {
     _editableValue = new EditableString(text: _value,
                                         onUpdated: _handleTextUpdated);
   }
 
   void _handleTextUpdated() {
-    setState(() {});
+    scheduleBuild();
     if (_value != _editableValue.text) {
       _value = _editableValue.text;
       if (onChanged != null)
         onChanged(_value);
     }
   }
 
   void didUnmount() {
     if (_isAttachedToKeyboard)
       keyboard.hide();
@@ skipping 16 matching lines @@
 
     children.add(new EditableText(value: _editableValue, focused: focused));
 
     return new Container(
       style: _style,
       inlineStyle: focused ? _focusedInlineStyle : null,
       children: children
     );
   }
 }