Add RenderObject.childCount

sky/sdk/lib/rendering/object.dart

Index: sky/sdk/lib/rendering/object.dart
diff --git a/sky/sdk/lib/rendering/object.dart b/sky/sdk/lib/rendering/object.dart
index a21db01421615485521d0d36a5e7c7a53cb57c5e..3e92d3d9204a073fd766e0f86c0b7593cd186a84 100644
--- a/sky/sdk/lib/rendering/object.dart
+++ b/sky/sdk/lib/rendering/object.dart
@@ -367,7 +367,6 @@ abstract class ContainerParentDataMixin<ChildType extends RenderObject> {
 }
 
 abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, ParentDataType extends ContainerParentDataMixin<ChildType>> implements RenderObject {
-  // abstract class that has only InlineNode children
 
   bool _debugUltimatePreviousSiblingOf(ChildType child, { ChildType equals }) {
     assert(child.parentData is ParentDataType);
@@ -388,12 +387,19 @@ abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, Parent
     return child == equals;
   }
 
+  int _childCount = 0;
+  int get childCount => _childCount;
+
   ChildType _firstChild;
   ChildType _lastChild;
   void _addToChildList(ChildType child, { ChildType before }) {
     assert(child.parentData is ParentDataType);
     assert(child.parentData.nextSibling == null);
     assert(child.parentData.previousSibling == null);
+
+    _childCount += 1;

[Hixie, 2015/06/26 18:04:33]

Since the rest of this function doesn't have paragraph breaks (and indeed, it's
in the same paragraph as the next function and the members defined before it),
it's weird to have newlines here.

[hansmuller, 2015/06/26 18:16:10]

Done.

+    assert(_childCount > 0);
+
     if (before == null) {
       // append at the end (_lastChild)
       child.parentData.previousSibling = _lastChild;
@@ -448,6 +454,10 @@ abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, Parent
     assert(child.parentData is ParentDataType);
     assert(_debugUltimatePreviousSiblingOf(child, equals: _firstChild));
     assert(_debugUltimateNextSiblingOf(child, equals: _lastChild));
+
+    _childCount -= 1;
+    assert(_childCount > 0);
+

[Hixie, 2015/06/26 18:04:33]

ditto here

[hansmuller, 2015/06/26 18:16:10]

Done.

     if (child.parentData.previousSibling == null) {
       assert(_firstChild == child);
       _firstChild = child.parentData.nextSibling;