Spinning Square example for the RenderObject API.

sky/sdk/lib/framework/rendering/box.dart

Index: sky/sdk/lib/framework/rendering/box.dart
diff --git a/sky/sdk/lib/framework/rendering/box.dart b/sky/sdk/lib/framework/rendering/box.dart
index 6b5d0f0d419cbbfa67b664f69779734f7f36c86f..1a38695ccb6e6b44a0de759b37c9f0029fca347a 100644
--- a/sky/sdk/lib/framework/rendering/box.dart
+++ b/sky/sdk/lib/framework/rendering/box.dart
@@ -916,7 +916,7 @@ class RenderTransform extends RenderProxyBox {
 
   Matrix4 _transform;
 
-  void set transform (Matrix4 value) {
+  void set transform(Matrix4 value) {
     assert(value != null);
     if (_transform == value)
       return;
@@ -924,6 +924,11 @@ class RenderTransform extends RenderProxyBox {
     markNeedsPaint();
   }
 
+  void setIdentity() {
+    _transform.setIdentity();
+    markNeedsPaint();
+  }
+
   void rotateX(double radians) {
     _transform.rotateX(radians);
     markNeedsPaint();