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

This adds a missing conversion of time zone names to string primitives
before case conversion and regular expression matching are applied.

This is in sync with ECMA-402, section 12.1.1.1, step 16(a).

R=jochen@chromium.org
TEST=mjsunit/regress/regress-crbug-627935
BUG=chromium:627935

Review-Url: https://codereview.chromium.org/2143003005
Cr-Commit-Position: refs/heads/master@{#37757}

src/js/i18n.js

@@ -1785,6 +1785,9 @@ function canonicalizeTimeZoneID(tzID) {
     return tzID;
   }
 
+  // Convert zone name to string.
+  tzID = TO_STRING(tzID);
+
   // Special case handling (UTC, GMT).
   var upperID = %StringToUpperCase(tzID);
   if (upperID === 'UTC' || upperID === 'GMT' ||

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

+// 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})");