Make toLocaleString on arrays always call toLocaleString on its elements.

test/mjsunit/es6/typedarray-tostring.js

 // Copyright 2015 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.
 
 // Array's toString should call the object's own join method, if one exists and
 // is callable. Otherwise, just use the original Object.toString function.
 
 var typedArrayConstructors = [
   Uint8Array,
   Int8Array,
@@ skipping 65 matching lines @@
 
   // Redefining length does not change result
   var a5 = new constructor([1, 2, 3])
   Object.defineProperty(a5, 'length', { value: 2 });
   assertEquals("1,2,3", a5.join());
   assertEquals("1,2,3", a5.toString());
   assertEquals("1,2,3", a5.toLocaleString());
   assertEquals("1,2", Array.prototype.join.call(a5));
   assertEquals("1,2,3", Array.prototype.toString.call(a5));
   assertEquals("1,2", Array.prototype.toLocaleString.call(a5));
+
+  (function TestToLocaleStringCalls() {
+    let log = [];
+    let pushArgs = (label) => (...args) => log.push(label, args);
+
+    let NumberToLocaleString = Number.prototype.toLocaleString;
+    Number.prototype.toLocaleString = pushArgs("Number");
+
+    (new constructor([1, 2])).toLocaleString();
+    assertEquals(["Number", [], "Number", []], log);
+
+    Number.prototype.toLocaleString = NumberToLocaleString;
+  })();
 }