Register JSFixedArray as instantiated.

tests/language/regress_27700_test.dart

Index: tests/language/regress_27700_test.dart
diff --git a/tests/language/regress_27700_test.dart b/tests/language/regress_27700_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..4366962bacaa8ab0cebfb7c02d52b95615d3fb5c
--- /dev/null
+++ b/tests/language/regress_27700_test.dart
@@ -0,0 +1,10 @@
+// Copyright (c) 2017, 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.
+
+// Regression test for issue 27700.
+
+main(){
+  var x = new List(0);
+  var z = "$x";
+}