Re-implement %Generator% intrinsic as an object

test/mjsunit/es6/generators-runtime.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 60 matching lines @@
 // Generators have an additional object interposed in the chain between
 // themselves and Function.prototype.
 function TestGeneratorFunctionPrototype() {
   // Sanity check.
   assertSame(Object.getPrototypeOf(f), Function.prototype);
   assertFalse(GeneratorFunctionPrototype === Function.prototype);
   assertSame(Function.prototype,
              Object.getPrototypeOf(GeneratorFunctionPrototype));
   assertSame(GeneratorFunctionPrototype,
              Object.getPrototypeOf(function* () {}));
+  assertSame("object", typeof GeneratorFunctionPrototype);
+
+  var constructor_desc = Object.getOwnPropertyDescriptor(
+      GeneratorFunctionPrototype, "constructor");
+  assertTrue(constructor_desc !== undefined);
+  assertSame(GeneratorFunction, constructor_desc.value);
+  assertFalse(constructor_desc.writable);
+  assertFalse(constructor_desc.enumerable);
+  assertTrue(constructor_desc.configurable);
+
+  var prototype_desc = Object.getOwnPropertyDescriptor(
+      GeneratorFunctionPrototype, "prototype");
+  assertTrue(prototype_desc !== undefined);
+  assertSame(GeneratorObjectPrototype, prototype_desc.value);
+  assertFalse(prototype_desc.writable);
+  assertFalse(prototype_desc.enumerable);
+  assertTrue(prototype_desc.configurable);
 }
 TestGeneratorFunctionPrototype();
 
 
 // Functions that we associate with generator objects are actually defined by
 // a common prototype.
 function TestGeneratorObjectPrototype() {
   assertSame(Object.prototype,
              Object.getPrototypeOf(GeneratorObjectPrototype));
   assertSame(GeneratorObjectPrototype,
@@ skipping 38 matching lines @@
 
   assertTrue((new GeneratorFunction()) instanceof GeneratorFunction);
   assertTrue(GeneratorFunction() instanceof GeneratorFunction);
 }
 TestGeneratorFunction();
 
 
 function TestPerGeneratorPrototype() {
   assertTrue((function*(){}).prototype !== (function*(){}).prototype);
   assertTrue((function*(){}).prototype !== g.prototype);
-  assertTrue(g.prototype instanceof GeneratorFunctionPrototype);
   assertSame(GeneratorObjectPrototype, Object.getPrototypeOf(g.prototype));
   assertTrue(!(g.prototype instanceof Function));
   assertSame(typeof (g.prototype), "object");
 
   assertArrayEquals([], Object.getOwnPropertyNames(g.prototype));
 }
 TestPerGeneratorPrototype();