Make generator constructors configurable

R=mstarzinger@chromium.org
BUG=v8:3902
LOG=Y

Review URL: https://codereview.chromium.org/939953002

Cr-Commit-Position: refs/heads/master@{#26744}

src/generator.js

@@ -97,7 +97,7 @@ function SetUpGenerators() {
   %AddNamedProperty(GeneratorObjectPrototype, symbolIterator,
       GeneratorObjectIterator, DONT_ENUM | DONT_DELETE | READ_ONLY);
   %AddNamedProperty(GeneratorObjectPrototype, "constructor",
-      GeneratorFunctionPrototype, DONT_ENUM | DONT_DELETE | READ_ONLY);
+      GeneratorFunctionPrototype, DONT_ENUM | READ_ONLY);
   %AddNamedProperty(GeneratorObjectPrototype,
       symbolToStringTag, "Generator", DONT_ENUM | READ_ONLY);
   %InternalSetPrototype(GeneratorFunctionPrototype, $Function.prototype);
@@ -105,7 +105,7 @@ function SetUpGenerators() {
       symbolToStringTag, "GeneratorFunction", DONT_ENUM | READ_ONLY);
   %SetCode(GeneratorFunctionPrototype, GeneratorFunctionPrototypeConstructor);
   %AddNamedProperty(GeneratorFunctionPrototype, "constructor",
-      GeneratorFunction, DONT_ENUM | DONT_DELETE | READ_ONLY);
+      GeneratorFunction, DONT_ENUM | READ_ONLY);
   %InternalSetPrototype(GeneratorFunction, $Function);
   %SetCode(GeneratorFunction, GeneratorFunctionConstructor);
 }

test/mjsunit/es6/regress/regress-3902.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.
+
+function* g() {}
+assertTrue(Object.getOwnPropertyDescriptor(g.__proto__, "constructor").configurable);
+assertTrue(Object.getOwnPropertyDescriptor(g.prototype.__proto__, "constructor").configurable);
+
+function FakeGeneratorFunctionConstructor() {}
+Object.defineProperty(g.__proto__, "constructor", {value: FakeGeneratorFunctionConstructor});
+assertSame(g.__proto__.constructor, FakeGeneratorFunctionConstructor);
+
+function FakeGeneratorObjectConstructor() {}
+Object.defineProperty(g.prototype.__proto__, "constructor", {value: FakeGeneratorObjectConstructor});
+assertSame(g.prototype.__proto__.constructor, FakeGeneratorObjectConstructor);