[Effen] Add a "parent" pointer to Node.

sky/sdk/lib/framework/layout.dart

Index: sky/sdk/lib/framework/layout.dart
diff --git a/sky/sdk/lib/framework/layout.dart b/sky/sdk/lib/framework/layout.dart
index 2580942222ad0d4fdad1cbff456fd3ccf6a72268..34566802c69b7856e425664f6a012699a83048e5 100644
--- a/sky/sdk/lib/framework/layout.dart
+++ b/sky/sdk/lib/framework/layout.dart
@@ -78,11 +78,11 @@ abstract class RenderNode extends Node {
       child.parentData = new ParentData();
   }
 
-  void setAsChild(RenderNode child) { // only for use by subclasses
+  void adoptChild(RenderNode child) { // only for use by subclasses
     // call this whenever you decide a node is a child
     assert(child != null);
     setupPos(child);
-    super.setAsChild(child);
+    super.adoptChild(child);
   }
   void dropChild(RenderNode child) { // only for use by subclasses
     assert(child != null);
@@ -149,7 +149,7 @@ abstract class ContainerRenderNodeMixin<ChildType extends RenderNode, ParentData
     assert(child != before);
     assert(child != _firstChild);
     assert(child != _lastChild);
-    setAsChild(child);
+    adoptChild(child);
     assert(child.parentData is ParentDataType);
     assert(child.parentData.nextSibling == null);
     assert(child.parentData.previousSibling == null);