Fix logic in RenderPadding.

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

Index: sky/sdk/lib/framework/rendering/block.dart
diff --git a/sky/sdk/lib/framework/rendering/block.dart b/sky/sdk/lib/framework/rendering/block.dart
index 8bc53939b53ba831b2d71003f6df6d1363f77e79..942b0de0d3e95df42273e24799bc4bc8c77ce142 100644
--- a/sky/sdk/lib/framework/rendering/block.dart
+++ b/sky/sdk/lib/framework/rendering/block.dart
@@ -14,6 +14,13 @@ class RenderBlock extends RenderBox with ContainerRenderNodeMixin<RenderBox, Blo
   // uses the maximum width provided by the parent
   // sizes itself to the height of its child stack
 
+  RenderBlock({
+    List<RenderBox> children
+  }) {
+    if (children != null)
+      children.forEach((child) { add(child); });
+  }
+
   void setParentData(RenderBox child) {
     if (child.parentData is! BlockParentData)
       child.parentData = new BlockParentData();