RenderObject.flushLayout should loop until _nodesNeedingLayout is empty

packages/flutter/lib/rendering/object.dart

@@ -407,12 +407,15 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
     sky.tracing.begin('RenderObject.flushLayout');
     _debugDoingLayout = true;
     try {
+      // TODO(ianh): assert that we're not allowing previously dirty nodes to redirty themeselves
+      while(_nodesNeedingLayout.isNotEmpty) {
         List<RenderObject> dirtyNodes = _nodesNeedingLayout;
         _nodesNeedingLayout = new List<RenderObject>();
         dirtyNodes..sort((a, b) => a.depth - b.depth)..forEach((node) {
           if (node._needsLayout && node.attached)
             node.layoutWithoutResize();
         });
+      }
     } finally {
       _debugDoingLayout = false;
       sky.tracing.end('RenderObject.flushLayout');