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

runtime/lib/growable_array.dart

Index: runtime/lib/growable_array.dart
diff --git a/runtime/lib/growable_array.dart b/runtime/lib/growable_array.dart
index 2a0ec8826c8a7fc24efa57cd982746f3db4e2d82..d3f76db6bdc3f630e7fc07cd3509e044bf4c20a0 100644
--- a/runtime/lib/growable_array.dart
+++ b/runtime/lib/growable_array.dart
@@ -336,8 +336,8 @@ class _GrowableList<T> implements List<T> {
     IterableMixinWorkaround.sortList(this, compare);
   }
 
-  void shuffle() {
-    IterableMixinWorkaround.shuffleList(this);
+  void shuffle([Random random]) {
+    IterableMixinWorkaround.shuffleList(this, random);
   }
 
   String toString() {