Fix the crash when the drawer is hidden.

sky/sdk/lib/framework/rendering/node.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 '../node.dart';
 import '../scheduler.dart' as scheduler;
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 
 class ParentData {
@@ skipping 37 matching lines @@
     // override this to setup .parentData correctly for your class
     if (child.parentData is! ParentData)
       child.parentData = new ParentData();
   }
 
   void adoptChild(RenderNode child) { // only for use by subclasses
     // call this whenever you decide a node is a child
     assert(child != null);
     setParentData(child);
     super.adoptChild(child);
+    markNeedsLayout();
   }
   void dropChild(RenderNode child) { // only for use by subclasses
     assert(child != null);
     assert(child.parentData != null);
     child.parentData.detach();
+    if (child._relayoutSubtreeRoot != child) {
+      child._relayoutSubtreeRoot = null;
+      child._needsLayout = true;
+    }
     super.dropChild(child);
+    markNeedsLayout();
   }
 
   static List<RenderNode> _nodesNeedingLayout = new List<RenderNode>();
   static bool _debugDoingLayout = false;
   bool _needsLayout = true;
   bool get needsLayout => _needsLayout;
   RenderNode _relayoutSubtreeRoot;
   dynamic _constraints;
   dynamic get constraints => _constraints;
   bool debugAncestorsAlreadyMarkedNeedsLayout() {
@@ skipping 150 matching lines @@
 
 abstract class RenderNodeWithChildMixin<ChildType extends RenderNode> {
   ChildType _child;
   ChildType get child => _child;
   void set child (ChildType value) {
     if (_child != null)
       dropChild(_child);
     _child = value;
     if (_child != null)
       adoptChild(_child);
-    markNeedsLayout();
   }
   void attachChildren() {
     if (_child != null)
       _child.attach();
   }
   void detachChildren() {
     if (_child != null)
       _child.detach();
   }
 }
@@ skipping 84 matching lines @@
         child.parentData.previousSibling = before.parentData.previousSibling;
         child.parentData.nextSibling = before;
         // set up links from siblings to child
         assert(child.parentData.previousSibling.parentData is ParentDataType);
         assert(child.parentData.nextSibling.parentData is ParentDataType);
         child.parentData.previousSibling.parentData.nextSibling = child;
         child.parentData.nextSibling.parentData.previousSibling = child;
         assert(before.parentData.previousSibling == child);
       }
     }
-    markNeedsLayout();
   }
   void remove(ChildType child) {
     assert(child.parentData is ParentDataType);
     assert(_debugUltimatePreviousSiblingOf(child, equals: _firstChild));
     assert(_debugUltimateNextSiblingOf(child, equals: _lastChild));
     if (child.parentData.previousSibling == null) {
       assert(_firstChild == child);
       _firstChild = child.parentData.nextSibling;
     } else {
       assert(child.parentData.previousSibling.parentData is ParentDataType);
       child.parentData.previousSibling.parentData.nextSibling = child.parentData.nextSibling;
     }
     if (child.parentData.nextSibling == null) {
       assert(_lastChild == child);
       _lastChild = child.parentData.previousSibling;
     } else {
       assert(child.parentData.nextSibling.parentData is ParentDataType);
       child.parentData.nextSibling.parentData.previousSibling = child.parentData.previousSibling;
     }
     child.parentData.previousSibling = null;
     child.parentData.nextSibling = null;
     dropChild(child);
-    markNeedsLayout();
   }
   void redepthChildren() {
     ChildType child = _firstChild;
     while (child != null) {
       redepthChild(child);
       assert(child.parentData is ParentDataType);
       child = child.parentData.nextSibling;
     }
   }
   void attachChildren() {
@@ skipping 13 matching lines @@
     }
   }
 
   ChildType get firstChild => _firstChild;
   ChildType get lastChild => _lastChild;
   ChildType childAfter(ChildType child) {
     assert(child.parentData is ParentDataType);
     return child.parentData.nextSibling;
   }
 }