Fix logic in RenderPadding.

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 b3ee6cddf6301afcd9e11f8c81bb8c84460ba568..a749a33379b567baa1cac0e04f874733946ef80c 100644
--- a/sky/sdk/lib/framework/rendering/box.dart
+++ b/sky/sdk/lib/framework/rendering/box.dart
@@ -4,6 +4,7 @@
 
 import 'node.dart';
 import 'dart:sky' as sky;
+import 'dart:math' as math;
 
 // GENERIC BOX RENDERING
 // Anything that has a concept of x, y, width, height is going to derive from this
@@ -40,11 +41,13 @@ class BoxConstraints {
 
   BoxConstraints deflate(EdgeDims edges) {
     assert(edges != null);
+    var horizontal = edges.left + edges.right;
+    var vertical = edges.top + edges.bottom;

[abarth-chromium, 2015/06/03 17:22:33]

s/var/double/

     return new BoxConstraints(
-      minWidth: minWidth,
-      maxWidth: maxWidth - (edges.left + edges.right),
-      minHeight: minHeight,
-      maxHeight: maxHeight - (edges.top + edges.bottom)
+      minWidth: math.min(0.0, minWidth - horizontal),
+      maxWidth: maxWidth - horizontal,
+      minHeight: math.min(0.0, minHeight - vertical),
+      maxHeight: maxHeight - vertical
     );
   }
 
@@ -171,7 +174,8 @@ class RenderSizedBox extends RenderProxyBox {
 
   void performLayout() {
     size = constraints.constrain(_desiredSize);
-    child.layout(new BoxConstraints.tight(size));
+    if (child != null)
+      child.layout(new BoxConstraints.tight(size));
   }
 }