Further ES2015 RegExp spec compliance fixes

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-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 affect string.replace
 // TODO(adamk): Add more tests here once we've switched
 // to use [[OriginalFlags]] in more cases.
 assertEquals(expected, string.replace(r3, "X"));
 assertEquals(5, get_count);
 
 
 function testName(name) {
-  // TODO(littledan): For web compatibility, we don't throw an exception,
-  // but ES2015 expects an exception to be thrown from this getter.
-  assertEquals(undefined, RegExp.prototype[name]);
+  // Test for ES2017 RegExp web compatibility semantics
+  // https://github.com/tc39/ecma262/pull/511
+  assertEquals(name === "source" ? "(?:)" : undefined,
+               RegExp.prototype[name]);
   assertEquals(
       "get " + name,
       Object.getOwnPropertyDescriptor(RegExp.prototype, name).get.name);
 }
 
 testName("global");
 testName("ignoreCase");
 testName("multiline");
 testName("source");
 testName("sticky");
@@ skipping 43 matching lines @@
   },
   get unicode() {
     map.u = counter++;
   },
   get sticky() {
     map.y = counter++;
   }
 };
 testGenericFlags(object);
 assertEquals({ g: 0, i: 1, m: 2, u: 3, y: 4 }, map);