[Intl] Fix subclassing of V8BreakIterator

Bug: v8:5751, chromium:881021
Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: I22514ceb5fb0953b728e67ba5266926e912ce9c1
Reviewed-on: https://chromium-review.googlesource.com/1208516Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55671}

src/objects.cc

@@ -13163,6 +13163,7 @@ bool CanSubclassHaveInobjectProperties(InstanceType instance_type) {
     case JS_INTL_NUMBER_FORMAT_TYPE:
     case JS_INTL_PLURAL_RULES_TYPE:
     case JS_INTL_RELATIVE_TIME_FORMAT_TYPE:
+    case JS_INTL_V8_BREAK_ITERATOR_TYPE:
 #endif
     case JS_ASYNC_GENERATOR_OBJECT_TYPE:
     case JS_MAP_TYPE:

test/intl/break-iterator/subclass.js

+// Copyright 2018 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.
+
+// Flags: --harmony-intl-list-format
+
+var locales = ["tlh", "id", "en"];
+var input = "foo and bar";
+var refBreakIterator = new Intl.v8BreakIterator(locales);
+refBreakIterator.adoptText(input);
+
+class MyBreakIterator extends Intl.v8BreakIterator {
+  constructor(locales, options) {
+    super(locales, options);
+  }
+}
+
+var myBreakIterator = new MyBreakIterator(locales);
+myBreakIterator.adoptText(input);
+
+let expectedPos = refBreakIterator.first();
+let actualPos = myBreakIterator.first();
+assertEquals(expectedPos, actualPos);
+
+while (expectedPos != -1) {
+  expectedPos = refBreakIterator.next();
+  actualPos = myBreakIterator.next();
+  assertEquals(expectedPos, actualPos);
+}