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 ee439632c1f90baf8c38004539c52d9e74ae4754..21d1878ffe30d33de4a9e40f25a8f3cd1707f24e 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;