Add web compat workarounds for ES2015 RegExp semantics

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 32 matching lines @@
 assertEquals(2, get_count);
 // Overridden flag getters affects the flags getter.
 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);
+  if (name === "sticky") {
+    assertEquals(undefined, RegExp.prototype[name]);
+  } else {
+    assertThrows(() => RegExp.prototype[name], TypeError);
+  }
   assertEquals(
       "get " + name,
       Object.getOwnPropertyDescriptor(RegExp.prototype, name).get.name);
 }
 
 testName("global");
 testName("ignoreCase");
 testName("multiline");
 testName("source");
 testName("sticky");
 testName("unicode");