[i18n] Ensure [[ToString]] conversion of time zone names.

test/mjsunit/regress/regress-crbug-627935.js

Index: test/mjsunit/regress/regress-crbug-627935.js
diff --git a/test/mjsunit/regress/regress-crbug-627935.js b/test/mjsunit/regress/regress-crbug-627935.js
new file mode 100644
index 0000000000000000000000000000000000000000..e958be0e302a6c436ba2a430517e029018ea54a3
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-627935.js
@@ -0,0 +1,10 @@
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+assertThrows("Intl.DateTimeFormat('en-US', {timeZone: 0})", RangeError);
+assertThrows("Intl.DateTimeFormat('en-US', {timeZone: true})", RangeError);
+assertThrows("Intl.DateTimeFormat('en-US', {timeZone: null})", RangeError);
+
+var object = { toString: function() { return "UTC" } };
+assertDoesNotThrow("Intl.DateTimeFormat('en-US', {timeZone: object})");