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

sdk/lib/_collection_dev/iterable.dart

Index: sdk/lib/_collection_dev/iterable.dart
diff --git a/sdk/lib/_collection_dev/iterable.dart b/sdk/lib/_collection_dev/iterable.dart
index 5001fe38fe20cefba1d83a18e521d7404e5a38c4..3cc913baa37eae41ef30921970ba3b3805939ef4 100644
--- a/sdk/lib/_collection_dev/iterable.dart
+++ b/sdk/lib/_collection_dev/iterable.dart
@@ -958,8 +958,8 @@ class IterableMixinWorkaround {
     Sort.sort(list, compare);
   }
 
-  static void shuffleList(List list) {
-    Random random = new Random();
+  static void shuffleList(List list, Random random) {
+    if (random == null) random = new Random();
     int length = list.length;
     while (length > 1) {
       int pos = random.nextInt(length);