Make FixedHeightScrollable understand heights

sky/sdk/lib/framework/fn2.dart

Index: sky/sdk/lib/framework/fn2.dart
diff --git a/sky/sdk/lib/framework/fn2.dart b/sky/sdk/lib/framework/fn2.dart
index 03206def57d7e72da18643c90c4344a0f380d933..7f8e303a63dbb8423a167a19da25ed52d307b415 100644
--- a/sky/sdk/lib/framework/fn2.dart
+++ b/sky/sdk/lib/framework/fn2.dart
@@ -421,6 +421,22 @@ class Transform extends OneChildRenderObjectWrapper {
   }
 }
 
+class SizeObserver extends OneChildRenderObjectWrapper {
+  RenderSizeObserver root;
+  final SizeChangedCallback callback;
+
+  SizeObserver({ this.callback, UINode child, Object key })
+    : super(child: child, key: key);
+
+  RenderSizeObserver createNode() => new RenderSizeObserver(callback: callback);
+
+  void syncRenderObject(SizeObserver old) {
+    super.syncRenderObject(old);
+    root.callback = callback;
+  }
+}

[Hixie, 2015/06/04 20:35:50]

Should probably drop the callback when the child is removed, too, in case the
RenderObject is actually used for something else later and ends up calling us
unexpectedly.

[abarth-chromium, 2015/06/04 20:41:25]

Done.

+
+
 final List<UINode> _emptyList = new List<UINode>();
 
 abstract class MultiChildRenderObjectWrapper extends RenderObjectWrapper {