Add @override annotation to known overriden methods

sky/sdk/example/widgets/styled_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 'package:sky/painting/text_style.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/sky_binding.dart';
 import 'package:sky/theme/colors.dart' as colors;
 import 'package:sky/widgets/basic.dart';
@@ skipping 31 matching lines @@
   List<List<String>> nameLines;
 
   final TextStyle daveStyle = new TextStyle(color: colors.Indigo[400], height: 1.8);
   final TextStyle halStyle = new TextStyle(color: colors.Red[400], fontFamily: "monospace");
   final TextStyle boldStyle = const TextStyle(fontWeight: bold);
   final TextStyle underlineStyle = const TextStyle(
     decoration: underline,
     decorationColor: const Color(0xFF000000),
     decorationStyle: TextDecorationStyle.wavy
   );
-  
+
   Component toStyledText(String name, String text) {
     TextStyle lineStyle = (name == "Dave") ? daveStyle : halStyle;
     return new StyledText(
       key: text,
       elements: [lineStyle, [boldStyle, [underlineStyle, name], ":"], text]
     );
   }
 
   Component toPlainText(String name, String text) => new Text(name + ":" + text);
 
   Component createSeparator() {
     return new Container(
       constraints: const BoxConstraints.expandWidth(maxHeight: 0.0),
       margin: const EdgeDims.symmetric(vertical: 10.0, horizontal: 64.0),
       decoration: const BoxDecoration(
         border: const Border(
           bottom: const BorderSide(color: const Color.fromARGB(24, 0, 0, 0))
         )
       )
     );
   }
 
   void toggleToTextFunction(_) {
     setState(() {
       toText = (toText == toPlainText) ? toStyledText : toPlainText;
     });
   }
 
+  @override
   Widget build() {
     List<Component> lines = nameLines
       .map((nameAndText) => Function.apply(toText, nameAndText))
       .toList();
 
     List<Component> children = [];
     for (Component line in lines) {
       children.add(line);
       if (line != lines.last) {
         children.add(createSeparator());
@@ skipping 29 matching lines @@
   }
 }
 
 void main() {
   runApp(new StyledTextApp());
   SkyBinding.instance.onFrame = () {
     // uncomment this for debugging:
     // SkyBinding.instance.debugDumpRenderTree();
   };
 }