Make 'where' lazy.

samples/swarm/swarm_ui_lib/layout/GridLayout.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Implements a grid-based layout system based on:
  * [http://dev.w3.org/csswg/css3-grid-align/]
  *
  * This layout is designed to support animations and work on browsers that
  * don't support grid natively. As such, we implement it on top of absolute
@@ skipping 236 matching lines @@
   /**
    * This method computes a '1fr' value, referred to as the
    * tempBreadth, for a set of Grid Tracks. The value computed
    * will ensure that when the tempBreadth is multiplied by the
    * fractions associated with tracks, that the UsedBreadths of tracks
    * will increase by an amount equal to the maximum of zero and the specified
    * freeSpace less the sum of the current UsedBreadths.
    */
   num _calcNormalizedFractionBreadth(List<GridTrack> tracks) {
 
-    final fractionTracks = tracks.where((t) => t.maxSizing.isFraction);
+    final fractionTracks = tracks.where((t) => t.maxSizing.isFraction).toList();
 
     // Note: the spec has various bugs in this function, such as mismatched
     // identifiers and names that aren't defined. For the most part it's
     // possible to figure out the meaning. It's also a bit confused about
     // how to compute spaceNeededFromFractionTracks, but that should just be the
     // set to the remaining free space after usedBreadth is accounted for.
 
     // We use the tempBreadth field to store the normalized fraction breadth
     for (final t in fractionTracks) {
       t.tempBreadth = t.usedBreadth / t.maxSizing.fractionValue;
@@ skipping 66 matching lines @@
    * in content-sized Grid Tracks by the Grid Item's spanCount. That is, Grid
    * Items having a lower spanCount have an opportunity to increase the size of
    * the Grid Tracks they cover before those with larger SpanCounts.
    *
    * Note: items are assumed to be already sorted in increasing span count
    */
   void _distributeSpaceBySpanCount(List<ViewLayout> items,
       ContentSizeMode sizeMode, _BreadthAccumulator breadth) {
 
     items = items.where((item) =>
-        _hasContentSizedTracks(_getTracks(item), sizeMode, breadth));
+        _hasContentSizedTracks(_getTracks(item), sizeMode, breadth)).toList();
 
     var tracks = [];
 
     for (int i = 0; i < items.length; i++) {
       final item = items[i];
 
       final itemTargetSize = item.measureContent(this, _dimension, sizeMode);
 
       final spannedTracks = _getTracks(item);
       _distributeSpaceToTracks(spannedTracks, itemTargetSize, breadth, true);
@@ skipping 155 matching lines @@
     }
     return result;
   }
 
   int _getSpanCount(ViewLayout item) {
     GridLayoutParams childLayout = item.layoutParams;
     return (_dimension == Dimension.WIDTH ?
         childLayout.columnSpan : childLayout.rowSpan);
   }
 }