Remove Collection references.

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.
 
 part of layout;
 
 /**
  * Implements a grid-based layout system based on:
  * [http://dev.w3.org/csswg/css3-grid-align/]
  *
@@ skipping 362 matching lines @@
         }
         tracks = [];
       }
     }
   }
 
   /**
    * Returns true if we have an appropriate content sized dimension, and don't
    * cross a fractional track.
    */
-  static bool _hasContentSizedTracks(Collection<GridTrack> tracks,
+  static bool _hasContentSizedTracks(Iterable<GridTrack> tracks,
       ContentSizeMode sizeMode, _BreadthAccumulator breadth) {
 
     for (final t in tracks) {
       final fn = breadth.getSizingFunction(t);
       if (sizeMode == ContentSizeMode.MAX && fn.isMaxContentSized ||
           sizeMode == ContentSizeMode.MIN && fn.isContentSized) {
 
         // Make sure we don't cross a fractional track
         return tracks.length == 1 || !tracks.any((t_) => t_.isFractional);
       }
@@ skipping 118 matching lines @@
     }
     return result;
   }
 
   int _getSpanCount(ViewLayout item) {
     GridLayoutParams childLayout = item.layoutParams;
     return (_dimension == Dimension.WIDTH ?
         childLayout.columnSpan : childLayout.rowSpan);
   }
 }