Instead of applying a transform for every RenderObject, pass down an Offset for where to paint.

sky/sdk/lib/widgets/tabs.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:math' as math;
 
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/icon.dart';
@@ skipping 113 matching lines @@
       child.parentData.position = new Point(x, 0.0);
       x += tabWidth;
       child = child.parentData.nextSibling;
     }
   }
 
   void hitTestChildren(HitTestResult result, { Point position }) {
     defaultHitTestChildren(result, position: position);
   }
 
-  void _paintIndicator(RenderCanvas canvas, RenderBox selectedTab) {
+  void _paintIndicator(RenderCanvas canvas, RenderBox selectedTab, Offset offset) {
     if (indicatorColor == null)
       return;
 
     var size = new Size(selectedTab.size.width, _kTabIndicatorHeight);
     var point = new Point(
       selectedTab.parentData.position.x,
-      _tabBarHeight - _kTabIndicatorHeight);
-    Rect rect = new Rect.fromPointAndSize(point, size);
+      _tabBarHeight - _kTabIndicatorHeight
+    );
+    Rect rect = new Rect.fromPointAndSize(point + offset, size);
     canvas.drawRect(rect, new Paint()..color = indicatorColor);
   }
 
-  void paint(RenderCanvas canvas) {
+  void paint(RenderCanvas canvas, Offset offset) {
     if (backgroundColor != null) {
-      Rect rect = new Rect.fromSize(size);
+      Rect rect = offset + size;
       canvas.drawRect(rect, new Paint()..color = backgroundColor);
     }
 
     int index = 0;
     RenderBox child = firstChild;
     while (child != null) {
       assert(child.parentData is TabBarParentData);
-      canvas.paintChild(child, child.parentData.position);
+      canvas.paintChild(child, child.parentData.position + offset);
       if (index++ == selectedIndex)
-        _paintIndicator(canvas, child);
+        _paintIndicator(canvas, child, offset);
       child = child.parentData.nextSibling;
     }
   }
 }
 
 class TabBarWrapper extends MultiChildRenderObjectWrapper {
   TabBarWrapper({
     List<Widget> children,
     this.selectedIndex,
     this.backgroundColor,
@@ skipping 123 matching lines @@
     }
     return new TabBarWrapper(
       children: tabs, 
       selectedIndex: selectedIndex,
       backgroundColor: Theme.of(this).primary[500],
       indicatorColor: Theme.of(this).accent[200],
       textAndIcons: textAndIcons
     );
   }
 }