Make arithmetic_test pass again on dart2js.

tests/language/left_shift_test.dart

Index: tests/language/left_shift_test.dart
===================================================================
--- tests/language/left_shift_test.dart	(revision 0)
+++ tests/language/left_shift_test.dart	(revision 0)
@@ -0,0 +1,11 @@
+// Copyright (c) 2012, 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.
+
+main() {
+  for (int i = 0; i < 80; i++) {
+    var a = -1 << i;
+    var b = -1;
+    Expect.equals(1 << i, a ~/ b);
+  }
+}