Make List.shuffle take an optional Random object to use.

sdk/lib/collection/list.dart

 // Copyright (c) 2013, 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 dart.collection;
 
 /**
  * Abstract implementation of a list.
  *
  * All operations are defined in terms of `length`, `operator[]`,
@@ skipping 283 matching lines @@
   }
 
   void sort([int compare(E a, E b)]) {
     if (compare == null) {
       var defaultCompare = Comparable.compare;
       compare = defaultCompare;
     }
     Sort.sort(this, compare);
   }
 
-  void shuffle() {
-    Random random = new Random();
+  void shuffle([Random random]) {
+    if (random == null) random = new Random();
     int length = this.length;
     while (length > 1) {
       int pos = random.nextInt(length);
       length -= 1;
       var tmp = this[length];
       this[length] = this[pos];
       this[pos] = tmp;
     }
   }
 
@@ skipping 182 matching lines @@
       result.writeAll(this, ', ');
       result.write(']');
      } finally {
        assert(identical(_toStringList.last, this));
        _toStringList.removeLast();
      }
 
     return result.toString();
   }
 }