Add List.shuffle().

sdk/lib/_collection_dev/list.dart

Index: sdk/lib/_collection_dev/list.dart
diff --git a/sdk/lib/_collection_dev/list.dart b/sdk/lib/_collection_dev/list.dart
index f5db3bbc7f898f4bfcfb67ea840cdb258ffc6f8a..6acc5d27af906f349f994c73cc78b03edb278360 100644
--- a/sdk/lib/_collection_dev/list.dart
+++ b/sdk/lib/_collection_dev/list.dart
@@ -140,6 +140,11 @@ abstract class UnmodifiableListMixin<E> implements List<E> {
         "Cannot modify an unmodifiable list");
   }
 
+  void shuffle() {
+    throw new UnsupportedError(
+        "Cannot modify an unmodifiable list");
+  }
+
   void clear() {
     throw new UnsupportedError(
         "Cannot clear an unmodifiable list");