fix for #520, ListMixin should work again

test/codegen/language/list_mixin_test.dart

Index: test/codegen/language/list_mixin_test.dart
diff --git a/test/codegen/language/list_mixin_test.dart b/test/codegen/language/list_mixin_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..5ae8563ec988800956641ab3493ac4fa0030b1ee
--- /dev/null
+++ b/test/codegen/language/list_mixin_test.dart
@@ -0,0 +1,16 @@
+import 'dart:collection';
+import 'package:expect/expect.dart';
+
+class MyList extends ListBase {
+  int get length => 4;
+  set length(int x) {}
+  int operator[](int x) => 42;
+  void operator[]=(int x, val) {}
+}
+
+main() {
+  var x = new MyList();
+  int z = 0;
+  x.forEach((y) { z += y; });
+  Expect.equals(z, 4 * 42);
+}