Further ES2015 RegExp spec compliance fixes

test/mjsunit/es6/regexp-constructor.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-regexp-subclass
 
 "use strict";
 
 function should_not_be_called() {
   throw new Error("should not be called");
 }
 
 (function() {
   var r = new RegExp("biep");
   assertTrue(r === RegExp(r));
   assertFalse(r === new RegExp(r));
   r[Symbol.match] = false;
   Object.defineProperty(r, "source", {get: should_not_be_called});
   Object.defineProperty(r, "flags", {get: should_not_be_called});
   assertFalse(r === RegExp(r));
 })();
 
 (function() {
+  let allow = false;
   class A extends RegExp {
-    get source() { throw new Error("should not be called") }
-    get flags() { throw new Error("should not be called") }
+    get source() {
+      if (!allow) throw new Error("should not be called");
+      return super.source;
+    }
+    get flags() {
+      if (!allow) throw new Error("should not be called");
+      return super.flags
+    }
   }
 
   var r = new A("biep");
   var r2 = RegExp(r);
 
   assertFalse(r === r2);
+  allow = true;
   assertEquals(r, r2);
+  allow = false;
   assertTrue(A.prototype === r.__proto__);
   assertTrue(RegExp.prototype === r2.__proto__);
 
   var r3 = RegExp(r);
   assertFalse(r3 === r);
+  allow = true;
   assertEquals(r3, r);
+  allow = false;
 
   var r4 = new A(r2);
   assertFalse(r4 === r2);
+  allow = true;
   assertEquals(r4, r2);
+  allow = false;
   assertTrue(A.prototype === r4.__proto__);
 
   r[Symbol.match] = false;
   var r5 = new A(r);
   assertFalse(r5 === r);
+  allow = true;
   assertEquals(r5, r);
+  allow = false;
   assertTrue(A.prototype === r5.__proto__);
 })();
 
 (function() {
   var log = [];
   var match = {
     get source() { log.push("source"); return "biep"; },
     get flags() { log.push("flags"); return "i"; }
   };
   Object.defineProperty(match, Symbol.match,
@@ skipping 30 matching lines @@
 (function() {
   class A extends RegExp {
     get ["constructor"]() { log.push("constructor"); return RegExp; }
   }
   var r = new A("biep");
   var log = [];
   var r2 = RegExp(r);
   assertEquals(["constructor"], log);
   assertTrue(r === r2);
 })();