Version 0 of TabLabel, Tab, and TabBar components

sky/sdk/lib/rendering/box.dart

Index: sky/sdk/lib/rendering/box.dart
diff --git a/sky/sdk/lib/rendering/box.dart b/sky/sdk/lib/rendering/box.dart
index 55017dc42323d2b6847830f9e5cfcf2172d16fcf..1d12c97eb50edff4e79773d3f1b1662bb9a43c64 100644
--- a/sky/sdk/lib/rendering/box.dart
+++ b/sky/sdk/lib/rendering/box.dart
@@ -163,6 +163,10 @@ class BoxConstraints extends Constraints {
                               maxHeight: math.min(maxHeight, newMaxHeight));
   }
 
+  BoxConstraints widthConstraints() => new BoxConstraints(minWidth: minWidth, maxWidth: maxWidth);
+
+  BoxConstraints heightConstraints() => new BoxConstraints(minHeight: minHeight, maxHeight: maxHeight);
+
   final double minWidth;
   final double maxWidth;
   final double minHeight;