[tests] Fix bogus uses of assertThrows.

test/mjsunit/es6/array-tostring.js

 // Copyright 2014 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-tostring
 
 var global = this;
 
 var funs = {
   Object:   [ Object ],
@@ skipping 23 matching lines @@
   var obj = {};
   obj[Symbol.toStringTag] = className;
   assertEquals("[object " + className + "]",
                Array.prototype.toString.call(obj));
 
   // Getter throws
   obj = {};
   Object.defineProperty(obj, Symbol.toStringTag, {
     get: function() { throw className; }
   });
-  assertThrows(function() {
+  assertThrowsEquals(function() {
     Array.prototype.toString.call(obj);
   }, className);
 
   // Getter does not throw
   obj = {};
   Object.defineProperty(obj, Symbol.toStringTag, {
     get: function() { return className; }
   });
   assertEquals("[object " + className + "]",
                Array.prototype.toString.call(obj));
@@ skipping 93 matching lines @@
   assertEquals(",,3", [,,3].toString());
 }
 testArrayToStringBasic();
 
 
 function testArrayToStringObjectWithCallableJoin() {
   var obj = { join: function() { return "CallableJoin"; } };
   assertEquals("CallableJoin", Array.prototype.toString.call(obj));
 }
 testArrayToStringObjectWithCallableJoin();