Add @override annotation to known overriden methods

sky/sdk/lib/rendering/object.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:math' as math;
 import 'dart:sky' as sky;
 import 'dart:sky' show Point, Offset, Size, Rect, Color, Paint, Path;
 
 import '../base/hit_test.dart';
 import '../base/node.dart';
 import '../base/scheduler.dart' as scheduler;
 
 export 'dart:sky' show Point, Offset, Size, Rect, Color, Paint, Path;
 export '../base/hit_test.dart' show HitTestTarget, HitTestEntry, HitTestResult;
 
 
 class ParentData {
   void detach() {
     detachSiblings();
   }
   void detachSiblings() { } // workaround for lack of inter-class mixins in Dart
   void merge(ParentData other) {
     // override this in subclasses to merge in data from other into this
     assert(other.runtimeType == this.runtimeType);
   }
+  @override
   String toString() => '<none>';
 }
 
 class PaintingCanvas extends sky.Canvas {
   PaintingCanvas(sky.PictureRecorder recorder, Rect bounds) : super(recorder, bounds);
 
   List<RenderObject> _descendentsWithPaintingCanvases = new List<RenderObject>(); // used by RenderObject._updatePaintingCanvas() to find out which RenderObjects to ask to paint
   void paintChild(RenderObject child, Point point) {
     if (child.createNewDisplayList) {
       assert(!_descendentsWithPaintingCanvases.contains(child));
@@ skipping 20 matching lines @@
   // node out, and any other nodes who happen to know exactly what
   // kind of node that is.
   dynamic parentData; // TODO(ianh): change the type of this back to ParentData once the analyzer is cleverer
   void setupParentData(RenderObject child) {
     // override this to setup .parentData correctly for your class
     assert(debugCanPerformMutations);
     if (child.parentData is! ParentData)
       child.parentData = new ParentData();
   }
 
+  @override
   void adoptChild(RenderObject child) { // only for use by subclasses
     // call this whenever you decide a node is a child
     assert(debugCanPerformMutations);
     assert(child != null);
     setupParentData(child);
     super.adoptChild(child);
     markNeedsLayout();
   }
+
+  @override
   void dropChild(RenderObject child) { // only for use by subclasses
     assert(debugCanPerformMutations);
     assert(child != null);
     assert(child.parentData != null);
     child._cleanRelayoutSubtreeRoot();
     child.parentData.detach();
     super.dropChild(child);
     markNeedsLayout();
   }
 
@@ skipping 320 matching lines @@
   //   // Otherwise:
   //   // For each child that intersects x,y, in z-order starting from the top,
   //   // call hitTest() for that child, passing it /result/, and the coordinates
   //   // converted to the child's coordinate origin, and stop at the first child
   //   // that returns true.
   //   // Then, add yourself to /result/, and return true.
   // }
   // You must not add yourself to /result/ if you return false.
 
 
+  @override
   String toString([String prefix = '']) {
     RenderObject debugPreviousActiveLayout = _debugActiveLayout;
     _debugActiveLayout = null;
     String header = '${runtimeType}';
     if (_relayoutSubtreeRoot != null && _relayoutSubtreeRoot != this) {
       int count = 1;
       RenderObject target = parent;
       while (target != null && target != _relayoutSubtreeRoot) {
         target = target.parent as RenderObject;
         count += 1;
@@ skipping 256 matching lines @@
     int count = 1;
     ChildType child = _firstChild;
     while (child != null) {
       result += '${prefix}child ${count}: ${child.toString(prefix)}';
       count += 1;
       child = child.parentData.nextSibling;
     }
     return result;
   }
 }