Add @override annotation to known overriden methods

sky/sdk/lib/rendering/block.dart

Index: sky/sdk/lib/rendering/block.dart
diff --git a/sky/sdk/lib/rendering/block.dart b/sky/sdk/lib/rendering/block.dart
index 3a1ea069f5788406b7cabce2abb83a163d9facef..9faf7a6131c22423e3c0388af631e1502f96eb01 100644
--- a/sky/sdk/lib/rendering/block.dart
+++ b/sky/sdk/lib/rendering/block.dart
@@ -21,6 +21,7 @@ abstract class RenderBlockBase extends RenderBox with ContainerRenderObjectMixin
     addAll(children);
   }
 
+  @override
   void setupParentData(RenderBox child) {
     if (child.parentData is! BlockParentData)
       child.parentData = new BlockParentData();
@@ -29,11 +30,13 @@ abstract class RenderBlockBase extends RenderBox with ContainerRenderObjectMixin
   double _childrenHeight;
   double get childrenHeight => _childrenHeight;
 
+  @override
   void markNeedsLayout() {
     _childrenHeight = null;
     super.markNeedsLayout();
   }
 
+  @override
   void performLayout() {
     assert(constraints is BoxConstraints);
     double width = constraints.constrainWidth(constraints.maxWidth);
@@ -58,6 +61,7 @@ class RenderBlock extends RenderBlockBase {
 
   RenderBlock({ List<RenderBox> children }) : super(children: children);
 
+  @override
   double getMinIntrinsicWidth(BoxConstraints constraints) {
     double width = 0.0;
     BoxConstraints innerConstraints = constraints.widthConstraints();
@@ -70,6 +74,7 @@ class RenderBlock extends RenderBlockBase {
     return width;
   }
 
+  @override
   double getMaxIntrinsicWidth(BoxConstraints constraints) {
     double width = 0.0;
     BoxConstraints innerConstraints = constraints.widthConstraints();
@@ -97,10 +102,12 @@ class RenderBlock extends RenderBlockBase {
     return height;
   }
 
+  @override
   double getMinIntrinsicHeight(BoxConstraints constraints) {
     return _getIntrinsicHeight(constraints);
   }
 
+  @override
   double getMaxIntrinsicHeight(BoxConstraints constraints) {
     return _getIntrinsicHeight(constraints);
   }
@@ -111,6 +118,7 @@ class RenderBlock extends RenderBlockBase {
 
   bool _hasVisualOverflow = false;
 
+  @override
   void performLayout() {
     super.performLayout();
     size = constraints.constrain(new Size(constraints.maxWidth, childrenHeight));
@@ -123,6 +131,7 @@ class RenderBlock extends RenderBlockBase {
     _hasVisualOverflow = childrenHeight > size.height;
   }
 
+  @override
   void paint(PaintingCanvas canvas, Offset offset) {
     if (_hasVisualOverflow) {
       canvas.save();
@@ -174,18 +183,22 @@ class RenderBlockViewport extends RenderBlockBase {
       markNeedsPaint();
   }
 
+  @override
   double getMinIntrinsicWidth(BoxConstraints constraints) {
     return constraints.constrainWidth();
   }
 
+  @override
   double getMaxIntrinsicWidth(BoxConstraints constraints) {
     return constraints.constrainWidth();
   }
 
+  @override
   double getMinIntrinsicHeight(BoxConstraints constraints) {
     return constraints.constrainHeight();
   }
 
+  @override
   double getMaxIntrinsicHeight(BoxConstraints constraints) {
     return constraints.constrainHeight();
   }
@@ -195,14 +208,18 @@ class RenderBlockViewport extends RenderBlockBase {
   // scroll the RenderBlockViewport, it would shift in its parent if
   // the parent was baseline-aligned, which makes no sense.
 
+  @override
   bool get sizedByParent => true;
 
+  @override
   void performResize() {
     size = constraints.biggest;
     assert(!size.isInfinite);
   }
 
   bool get debugDoesLayoutWithCallback => true;
+
+  @override
   void performLayout() {
     if (_callback != null) {
       try {
@@ -215,6 +232,7 @@ class RenderBlockViewport extends RenderBlockBase {
     super.performLayout();
   }
 
+  @override
   void paint(PaintingCanvas canvas, Offset offset) {
     canvas.save();
     canvas.clipRect(offset & size);
@@ -222,6 +240,7 @@ class RenderBlockViewport extends RenderBlockBase {
     canvas.restore();
   }
 
+  @override
   void hitTestChildren(HitTestResult result, { Point position }) {
     defaultHitTestChildren(result, position: position + new Offset(0.0, -startOffset));
   }