Add @override annotation to known overriden methods

sky/sdk/lib/widgets/widget.dart

Index: sky/sdk/lib/widgets/widget.dart
diff --git a/sky/sdk/lib/widgets/widget.dart b/sky/sdk/lib/widgets/widget.dart
index b099a3a98df227e31c9001cb19afdf107a47fb14..3cbb28078c1ad26b2345ed9228ebcec61b2ea089 100644
--- a/sky/sdk/lib/widgets/widget.dart
+++ b/sky/sdk/lib/widgets/widget.dart
@@ -207,6 +207,7 @@ abstract class Widget {
     return newNode;
   }
 
+  @override
   String toString([String prefix = '', String startPrefix = '']) {
     String childrenString = '';
     List<Widget> children = new List<Widget>();
@@ -246,11 +247,13 @@ abstract class TagNode extends Widget {
 
   Widget child;
 
+  @override
   void walkChildren(WidgetTreeWalker walker) {
     if (child != null)
       walker(child);
   }
 
+  @override
   void _sync(Widget old, dynamic slot) {
     Widget oldChild = old == null ? null : (old as TagNode).child;
     child = syncChild(child, oldChild, slot);
@@ -260,16 +263,19 @@ abstract class TagNode extends Widget {
     assert(_root == root); // in case a subclass reintroduces it
   }
 
+  @override
   void updateSlot(dynamic newSlot) {
     child.updateSlot(newSlot);
   }
 
+  @override
   void remove() {
     if (child != null)
       removeChild(child);
     super.remove();
   }
 
+  @override
   void detachRoot() {
     if (child != null)
       child.detachRoot();
@@ -287,6 +293,7 @@ abstract class Inherited extends TagNode {
 
   Inherited({ String key, Widget child }) : super._withKey(child, key);
 
+  @override
   void _sync(Widget old, dynamic slot) {
     if (old != null && syncShouldNotify(old)) {
       final Type ourRuntimeType = runtimeType;
@@ -413,17 +420,20 @@ abstract class Component extends Widget {
   Widget _built;
   dynamic _slot; // cached slot from the last time we were synced
 
+  @override
   void updateSlot(dynamic newSlot) {
     _slot = newSlot;
     if (_built != null)
       _built.updateSlot(newSlot);
   }
 
+  @override
   void walkChildren(WidgetTreeWalker walker) {
     if (_built != null)
       walker(_built);
   }
 
+  @override
   void remove() {
     assert(_built != null);
     assert(root != null);
@@ -432,6 +442,7 @@ abstract class Component extends Widget {
     super.remove();
   }
 
+  @override
   void detachRoot() {
     assert(_built != null);
     assert(root != null);
@@ -468,6 +479,7 @@ abstract class Component extends Widget {
   //      assert(_built != null && old == null)
   // 3) Syncing against an old version
   //      assert(_built == null && old != null)
+  @override
   void _sync(Component old, dynamic slot) {
     assert(_built == null || old == null);
 
@@ -522,26 +534,31 @@ abstract class StatefulComponent extends Component {
 
   bool _disqualifiedFromEverAppearingAgain = false;
 
+  @override
   void didMount() {
     assert(!_disqualifiedFromEverAppearingAgain);
     super.didMount();
   }
 
+  @override
   void _buildIfDirty() {
     assert(!_disqualifiedFromEverAppearingAgain);
     super._buildIfDirty();
   }
 
+  @override
   void _sync(Widget old, dynamic slot) {
     assert(!_disqualifiedFromEverAppearingAgain);
     super._sync(old, slot);
   }
 
+  @override
   Widget syncChild(Widget node, Widget oldNode, dynamic slot) {
     assert(!_disqualifiedFromEverAppearingAgain);
     return super.syncChild(node, oldNode, slot);
   }
 
+  @override
   bool retainStatefulNodeIfPossible(StatefulComponent newNode) {
     assert(!_disqualifiedFromEverAppearingAgain);
     assert(newNode != null);
@@ -678,6 +695,7 @@ abstract class RenderObjectWrapper extends Widget {
     newNode._ancestor = _ancestor;
   }
 
+  @override
   void _sync(RenderObjectWrapper old, dynamic slot) {
     // TODO(abarth): We should split RenderObjectWrapper into two pieces so that
     //               RenderViewObject doesn't need to inherit all this code it
@@ -702,6 +720,7 @@ abstract class RenderObjectWrapper extends Widget {
     syncRenderObject(old);
   }
 
+  @override
   void updateSlot(dynamic newSlot) {
     // We never use the slot except during sync(), in which
     // case our parent is handing it to us anyway.
@@ -729,12 +748,14 @@ abstract class RenderObjectWrapper extends Widget {
     }
   }
 
+  @override
   void remove() {
     assert(root != null);
     _nodeMap.remove(root);
     super.remove();
   }
 
+  @override
   void detachRoot() {
     assert(_ancestor != null);
     assert(root != null);
@@ -747,10 +768,12 @@ abstract class LeafRenderObjectWrapper extends RenderObjectWrapper {
 
   LeafRenderObjectWrapper({ String key }) : super(key: key);
 
+  @override
   void insertChildRoot(RenderObjectWrapper child, dynamic slot) {
     assert(false);
   }
 
+  @override
   void detachChildRoot(RenderObjectWrapper child) {
     assert(false);
   }
@@ -765,11 +788,13 @@ abstract class OneChildRenderObjectWrapper extends RenderObjectWrapper {
   Widget _child;
   Widget get child => _child;
 
+  @override
   void walkChildren(WidgetTreeWalker walker) {
     if (child != null)
       walker(child);
   }
 
+  @override
   void syncRenderObject(RenderObjectWrapper old) {
     super.syncRenderObject(old);
     Widget oldChild = old == null ? null : (old as OneChildRenderObjectWrapper).child;
@@ -779,6 +804,7 @@ abstract class OneChildRenderObjectWrapper extends RenderObjectWrapper {
     assert(oldChild == null || child == oldChild || oldChild.parent == null);
   }
 
+  @override
   void insertChildRoot(RenderObjectWrapper child, dynamic slot) {
     final root = this.root; // TODO(ianh): Remove this once the analyzer is cleverer
     assert(root is RenderObjectWithChildMixin);
@@ -787,6 +813,7 @@ abstract class OneChildRenderObjectWrapper extends RenderObjectWrapper {
     assert(root == this.root); // TODO(ianh): Remove this once the analyzer is cleverer
   }
 
+  @override
   void detachChildRoot(RenderObjectWrapper child) {
     final root = this.root; // TODO(ianh): Remove this once the analyzer is cleverer
     assert(root is RenderObjectWithChildMixin);
@@ -795,6 +822,7 @@ abstract class OneChildRenderObjectWrapper extends RenderObjectWrapper {
     assert(root == this.root); // TODO(ianh): Remove this once the analyzer is cleverer
   }
 
+  @override
   void remove() {
     if (child != null)
       removeChild(child);
@@ -815,11 +843,13 @@ abstract class MultiChildRenderObjectWrapper extends RenderObjectWrapper {
 
   final List<Widget> children;
 
+  @override
   void walkChildren(WidgetTreeWalker walker) {
     for (Widget child in children)
       walker(child);
   }
 
+  @override
   void insertChildRoot(RenderObjectWrapper child, dynamic slot) {
     final root = this.root; // TODO(ianh): Remove this once the analyzer is cleverer
     assert(slot == null || slot is RenderObject);
@@ -828,6 +858,7 @@ abstract class MultiChildRenderObjectWrapper extends RenderObjectWrapper {
     assert(root == this.root); // TODO(ianh): Remove this once the analyzer is cleverer
   }
 
+  @override
   void detachChildRoot(RenderObjectWrapper child) {
     final root = this.root; // TODO(ianh): Remove this once the analyzer is cleverer
     assert(root is ContainerRenderObjectMixin);
@@ -836,6 +867,7 @@ abstract class MultiChildRenderObjectWrapper extends RenderObjectWrapper {
     assert(root == this.root); // TODO(ianh): Remove this once the analyzer is cleverer
   }
 
+  @override
   void remove() {
     assert(children != null);
     for (var child in children) {
@@ -859,6 +891,7 @@ abstract class MultiChildRenderObjectWrapper extends RenderObjectWrapper {
     return false;
   }
 
+  @override
   void syncRenderObject(MultiChildRenderObjectWrapper old) {
     super.syncRenderObject(old);
 
@@ -1006,6 +1039,7 @@ class WidgetSkyBinding extends SkyBinding {
     assert(SkyBinding.instance is WidgetSkyBinding);
   }
 
+  @override
   void dispatchEvent(sky.Event event, HitTestResult result) {
     assert(SkyBinding.instance == this);
     super.dispatchEvent(event, result);
@@ -1033,16 +1067,19 @@ abstract class App extends StatefulComponent {
       onBack();
   }
 
+  @override
   void didMount() {
     super.didMount();
     SkyBinding.instance.addEventListener(_handleEvent);
   }
 
+  @override
   void didUnmount() {
     super.didUnmount();
     SkyBinding.instance.removeEventListener(_handleEvent);
   }
 
+  @override
   void syncFields(Component source) { }
 
   // Override this to handle back button behavior in your app
@@ -1059,11 +1096,13 @@ abstract class AbstractWidgetRoot extends StatefulComponent {
     _scheduleComponentForRender(this);
   }
 
+  @override
   void syncFields(AbstractWidgetRoot source) {
     assert(false);
     // if we get here, it implies that we have a parent
   }
 
+  @override
   void _buildIfDirty() {
     assert(_dirty);
     assert(_mounted);
@@ -1075,7 +1114,11 @@ abstract class AbstractWidgetRoot extends StatefulComponent {
 
 class RenderViewWrapper extends OneChildRenderObjectWrapper {
   RenderViewWrapper({ String key, Widget child }) : super(key: key, child: child);
+
+  @override
   RenderView get root => super.root;
+
+  @override
   RenderView createNode() => SkyBinding.instance.renderView;
 }
 
@@ -1084,6 +1127,8 @@ class AppContainer extends AbstractWidgetRoot {
     assert(SkyBinding.instance is WidgetSkyBinding);
   }
   final App app;
+
+  @override
   Widget build() => new RenderViewWrapper(child: app);
 }
 
@@ -1125,6 +1170,7 @@ class RenderBoxToWidgetAdapter extends AbstractWidgetRoot {
 
   final Builder builder;
 
+  @override
   void _buildIfDirty() {
     super._buildIfDirty();
     if (root.parent == null) {
@@ -1135,5 +1181,6 @@ class RenderBoxToWidgetAdapter extends AbstractWidgetRoot {
     assert(root.parent == _container);
   }
 
+  @override
   Widget build() => builder();
 }