Unify setting accessor properties in native code.

test/mjsunit/es6/regexp-flags.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.
 
 // Flags: --harmony-regexps --harmony-unicode-regexps
 
 var r1 = /abc/gi;
 assertEquals("abc", r1.source);
 assertTrue(r1.global);
 assertTrue(r1.ignoreCase);
@@ skipping 34 matching lines @@
 assertEquals("gi", r3.flags);
 assertEquals(4, get_count);
 // Overridden flag getters do not affect the internal flags.
 assertEquals(expected, string.replace(r3, "X"));
 assertEquals(4, get_count);
 
 
 function testName(name) {
   assertThrows(() => RegExp.prototype[name], TypeError);
   assertEquals(
-      "RegExp.prototype." + name,
+      "get " + name,
       Object.getOwnPropertyDescriptor(RegExp.prototype, name).get.name);
 }
 
 testName("global");
 testName("ignoreCase");
 testName("multiline");
 testName("source");
 testName("sticky");
 testName("unicode");