Add @override annotation to known overriden methods

sky/sdk/lib/painting/box_painter.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:math' as math;
 import 'dart:sky' as sky;
 import 'dart:sky' show Point, Offset, Size, Rect, Color, Paint, Path;
 
 import '../base/lerp.dart';
 import 'shadows.dart';
 
 class BorderSide {
   const BorderSide({
     this.color: const Color(0xFF000000),
     this.width: 1.0
   });
   final Color color;
   final double width;
 
   static const none = const BorderSide(width: 0.0);
 
+  @override
   int get hashCode {
     int value = 373;
     value = 37 * value * color.hashCode;
     value = 37 * value * width.hashCode;
     return value;
   }
+
+  @override
   String toString() => 'BorderSide($color, $width)';
 }
 
 class Border {
   const Border({
     this.top: BorderSide.none,
     this.right: BorderSide.none,
     this.bottom: BorderSide.none,
     this.left: BorderSide.none
   });
 
   const Border.all(BorderSide side) :
     top = side,
     right = side,
     bottom = side,
     left = side;
 
   final BorderSide top;
   final BorderSide right;
   final BorderSide bottom;
   final BorderSide left;
 
+  @override
   int get hashCode {
     int value = 373;
     value = 37 * value * top.hashCode;
     value = 37 * value * right.hashCode;
     value = 37 * value * bottom.hashCode;
     value = 37 * value * left.hashCode;
     return value;
   }
+
+  @override
   String toString() => 'Border($top, $right, $bottom, $left)';
 }
 
 class BoxShadow {
   const BoxShadow({
     this.color,
     this.offset,
     this.blur
   });
 
   final Color color;
   final Offset offset;
   final double blur;
 
+  @override
   String toString() => 'BoxShadow($color, $offset, $blur)';
 }
 
 BoxShadow lerpBoxShadow(BoxShadow a, BoxShadow b, double t) {
   return new BoxShadow(
       color: lerpColor(a.color, b.color, t),
       offset: lerpOffset(a.offset, b.offset, t),
       blur: lerpNum(a.blur, b.blur, t));
 }
 
 abstract class Gradient {
   sky.Shader createShader();
 }
 
 class LinearGradient extends Gradient {
   LinearGradient({
     this.endPoints,
     this.colors,
     this.colorStops,
     this.tileMode: sky.TileMode.clamp
   });
 
+  @override
   String toString() =>
       'LinearGradient($endPoints, $colors, $colorStops, $tileMode)';
 
+  @override
   sky.Shader createShader() {
     return new sky.Gradient.linear(this.endPoints, this.colors, this.colorStops,
                                    this.tileMode);
   }
 
   final List<Point> endPoints;
   final List<Color> colors;
   final List<double> colorStops;
   final sky.TileMode tileMode;
 }
 
 class RadialGradient extends Gradient {
   RadialGradient({
     this.center,
     this.radius,
     this.colors,
     this.colorStops,
     this.tileMode: sky.TileMode.clamp
   });
 
+  @override
   String toString() =>
       'RadialGradient($center, $radius, $colors, $colorStops, $tileMode)';
 
+  @override
   sky.Shader createShader() {
     return new sky.Gradient.radial(this.center, this.radius, this.colors,
                                    this.colorStops, this.tileMode);
   }
 
   final Point center;
   final double radius;
   final List<Color> colors;
   final List<double> colorStops;
   final sky.TileMode tileMode;
@@ skipping 35 matching lines @@
   final List<Function> _listeners = new List<Function>();
 
   void addChangeListener(Function listener) {
     _listeners.add(listener);
   }
 
   void removeChangeListener(Function listener) {
     _listeners.remove(listener);
   }
 
+  @override
   String toString() => 'BackgroundImage($fit, $repeat)';
 }
 
 enum Shape { rectangle, circle }
 
 // This must be immutable, because we won't notice when it changes
 class BoxDecoration {
   const BoxDecoration({
     this.backgroundColor, // null = don't draw background color
     this.backgroundImage, // null = don't draw background image
     this.border, // null = don't draw border
     this.borderRadius, // null = use more efficient background drawing; note that this must be null for circles
     this.boxShadow, // null = don't draw shadows
     this.gradient, // null = don't allocate gradient objects
     this.shape: Shape.rectangle
   });
 
   final Color backgroundColor;
   final BackgroundImage backgroundImage;
   final double borderRadius;
   final Border border;
   final List<BoxShadow> boxShadow;
   final Gradient gradient;
   final Shape shape;
 
+  @override
   String toString([String prefix = '']) {
     List<String> result = [];
     if (backgroundColor != null)
       result.add('${prefix}backgroundColor: $backgroundColor');
     if (backgroundImage != null)
       result.add('${prefix}backgroundImage: $backgroundImage');
     if (border != null)
       result.add('${prefix}border: $border');
     if (borderRadius != null)
       result.add('${prefix}borderRadius: $borderRadius');
@@ skipping 169 matching lines @@
     path.close();
     canvas.drawPath(path, paint);
   }
 
   void paint(sky.Canvas canvas, Rect rect) {
     _paintBackgroundColor(canvas, rect);
     _paintBackgroundImage(canvas, rect);
     _paintBorder(canvas, rect);
   }
 }