Remove redundant setState() calls around scroll behaviour updates.

sky/sdk/lib/widgets/variable_height_scrollable.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 'dart:collection';
 
 import 'package:sky/animation/scroll_behavior.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/block_viewport.dart';
 import 'package:sky/widgets/scrollable.dart';
@@ skipping 12 matching lines @@
   void syncFields(VariableHeightScrollable source) {
     builder = source.builder;
     token = source.token;
     super.syncFields(source);
   }
 
   ScrollBehavior createScrollBehavior() => new OverscrollBehavior();
   OverscrollBehavior get scrollBehavior => super.scrollBehavior;
 
   void _handleSizeChanged(Size newSize) {
-    setState(() {
-      scrollBehavior.containerSize = newSize.height;
-    });
+    scrollBehavior.containerSize = newSize.height;

[hansmuller, 2015/07/13 19:03:53]

If the viewport's size changes, don't you want to layout/paint?

   }
 
   void _handleLayoutChanged(
-      int firstVisibleChildIndex,
-      int visibleChildCount,
-      UnmodifiableListView<double> childOffsets,
-      bool didReachLastChild) {
+    int firstVisibleChildIndex,
+    int visibleChildCount,
+    UnmodifiableListView<double> childOffsets,
+    bool didReachLastChild
+  ) {
     assert(childOffsets.length > 0);
     scrollBehavior.contentsSize = didReachLastChild ? childOffsets.last : double.INFINITY;
     if (didReachLastChild && scrollOffset > scrollBehavior.maxScrollOffset)
       settleScrollOffset();
   }
 
   Widget buildContent() {
     return new SizeObserver(
       callback: _handleSizeChanged,
       child: new BlockViewport(
         builder: builder,
         onLayoutChanged: _handleLayoutChanged,
         startOffset: scrollOffset,
         token: token
       )
     );
   }
 }