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runtime/observatory/lib/src/elements/containers/virtual_collection.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. 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:async';
 import 'dart:html';
 import 'package:observatory/src/elements/helpers/rendering_scheduler.dart';
 import 'package:observatory/src/elements/helpers/tag.dart';
 
 typedef HtmlElement VirtualCollectionCreateCallback();
-typedef void VirtualCollectionUpdateCallback(HtmlElement el, dynamic item,
-    int index);
+typedef void VirtualCollectionUpdateCallback(
+    HtmlElement el, dynamic item, int index);
 
 class VirtualCollectionElement extends HtmlElement implements Renderable {
-  static const tag =
-      const Tag<VirtualCollectionElement>('virtual-collection');
+  static const tag = const Tag<VirtualCollectionElement>('virtual-collection');
 
   RenderingScheduler<VirtualCollectionElement> _r;
 
   Stream<RenderedEvent<VirtualCollectionElement>> get onRendered =>
       _r.onRendered;
 
   VirtualCollectionCreateCallback _create;
   VirtualCollectionCreateCallback _createHeader;
   VirtualCollectionUpdateCallback _update;
   double _itemHeight;
   double _headerHeight = 0.0;
   int _top;
   double _height;
   List _items;
   StreamSubscription _onScrollSubscription;
   StreamSubscription _onResizeSubscription;
 
   List get items => _items;
 
   set items(Iterable value) {
     _items = new List.unmodifiable(value);
     _top = null;
     _r.dirty();
   }
 
-
   factory VirtualCollectionElement(VirtualCollectionCreateCallback create,
-      VirtualCollectionUpdateCallback update, {Iterable items: const [],
+      VirtualCollectionUpdateCallback update,
+      {Iterable items: const [],
       VirtualCollectionCreateCallback createHeader,
       RenderingQueue queue}) {
     assert(create != null);
     assert(update != null);
     assert(items != null);
     VirtualCollectionElement e = document.createElement(tag.name);
     e._r = new RenderingScheduler(e, queue: queue);
     e._create = create;
     e._createHeader = createHeader;
     e._update = update;
     e._items = new List.unmodifiable(items);
     return e;
   }
 
   VirtualCollectionElement.created() : super.created();
 
   @override
   attached() {
     super.attached();
     _r.enable();
     _top = null;
     _itemHeight = null;
     _onScrollSubscription = onScroll.listen(_onScroll);
     _onResizeSubscription = window.onResize.listen(_onResize);
   }
 
- @override
+  @override
   detached() {
     super.detached();
     _r.disable(notify: true);
     children = const [];
     _onScrollSubscription.cancel();
     _onResizeSubscription.cancel();
   }
 
   final DivElement _header = new DivElement()..classes = ['header'];
   final DivElement _scroller = new DivElement()..classes = ['scroller'];
   final DivElement _shifter = new DivElement()..classes = ['shifter'];
 
   dynamic getItemFromElement(HtmlElement element) {
     final el_index = _shifter.children.indexOf(element);
     if (el_index < 0) {
       return null;
     }
     final item_index =
-      _top + el_index - (_shifter.children.length * _inverse_preload).floor();
+        _top + el_index - (_shifter.children.length * _inverse_preload).floor();
     if (0 <= item_index && item_index < items.length) {
       return _items[item_index];
     }
     return null;
   }
 
   /// The preloaded element before and after the visible area are:
   /// 1/preload_size of the number of items in the visble area.
   /// See shared.css for the "top:-25%;".
   static const int _preload = 2;
+
   /// L = length of all the elements loaded
   /// l = length of the visible area
   ///
   /// L = l + 2 * l / _preload
   /// l = L * _preload / (_preload + 2)
   ///
   /// tail = l / _preload = L * 1 / (_preload + 2) = L * _inverse_preload
   static const double _inverse_preload = 1 / (_preload + 2);
 
   var _takeIntoView;
 
   void takeIntoView(item) {
     _takeIntoView = item;
     _r.dirty();
   }
 
   void render() {
     if (children.isEmpty) {
       children = [
         _scroller
           ..children = [
-            _shifter
-              ..children = [_create()]
+            _shifter..children = [_create()]
           ],
       ];
       if (_createHeader != null) {
         _header.children = [_createHeader()];
         _scroller.children.insert(0, _header);
         _headerHeight = _header.children[0].getBoundingClientRect().height;
       }
       _itemHeight = _shifter.children[0].getBoundingClientRect().height;
       _height = getBoundingClientRect().height;
     }
@@ skipping 45 matching lines @@
   }
 
   void _onResize(_) {
     final newHeight = getBoundingClientRect().height;
     if (newHeight > _height) {
       _height = newHeight;
       _r.dirty();
     }
   }
 }