Add RenderObject.childCount

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 45 matching lines @@
 
   void setupParentData(RenderBox child) {
     if (child.parentData is! TabBarParentData)
       child.parentData = new TabBarParentData();
   }
 
   double getMinIntrinsicWidth(BoxConstraints constraints) {
     BoxConstraints widthConstraints =
         new BoxConstraints(maxWidth: constraints.maxWidth, maxHeight: constraints.maxHeight);
     double maxWidth = 0.0;
-    int childCount = 0;
     RenderBox child = firstChild;
     while (child != null) {
       maxWidth = math.max(maxWidth, child.getMinIntrinsicWidth(widthConstraints));
-      ++childCount;
       assert(child.parentData is TabBarParentData);
       child = child.parentData.nextSibling;
     }
     return constraints.constrainWidth(maxWidth * childCount);
   }
 
   double getMaxIntrinsicWidth(BoxConstraints constraints) {
     BoxConstraints widthConstraints =
         new BoxConstraints(maxWidth: constraints.maxWidth, maxHeight: constraints.maxHeight);
     double maxWidth = 0.0;
-    int childCount = 0;
     RenderBox child = firstChild;
     while (child != null) {
       maxWidth = math.max(maxWidth, child.getMaxIntrinsicWidth(widthConstraints));
-      ++childCount;
       assert(child.parentData is TabBarParentData);
       child = child.parentData.nextSibling;
     }
     return constraints.constrainWidth(maxWidth * childCount);
   }
 
   double _getIntrinsicHeight(BoxConstraints constraints) => constraints.constrainHeight(_kTabBarHeight);
 
   double getMinIntrinsicHeight(BoxConstraints constraints) => _getIntrinsicHeight(constraints);
 
   double getMaxIntrinsicHeight(BoxConstraints constraints) => _getIntrinsicHeight(constraints);
 
-  // TODO(hansmuller): track this value in the parent rather than computing it.
-  int _childCount() {
-    int childCount = 0;
-    RenderBox child = firstChild;
-    while (child != null) {
-      ++childCount;
-      assert(child.parentData is TabBarParentData);
-      child = child.parentData.nextSibling;
-    }
-    return childCount;
-  }
-
   void performLayout() {
     assert(constraints is BoxConstraints);
 
     size = constraints.constrain(new Size(constraints.maxWidth, _kTabBarHeight));
     assert(!size.isInfinite);
 
-    int childCount = _childCount();
     if (childCount == 0)
       return;
 
     double tabWidth = size.width / childCount;
     BoxConstraints tabConstraints =
       new BoxConstraints.tightFor(width: tabWidth, height: size.height);
     double x = 0.0;
     RenderBox child = firstChild;
     while (child != null) {
       child.layout(tabConstraints);
@@ skipping 156 matching lines @@
     return new TabBarWrapper(
       children: tabs, 
       selectedIndex: selectedIndex,
       backgroundColor: Theme.of(this).primary[500],
       indicatorColor: Theme.of(this).accent[200]
     );
   }
 }