[es6] Define generator prototype as writable prop

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 34 matching lines @@
 
   f_own_property_names.sort();
   g_own_property_names.sort();
 
   assertArrayEquals(f_own_property_names, g_own_property_names);
   var i;
   for (i = 0; i < f_own_property_names.length; i++) {
     var prop = f_own_property_names[i];
     var f_desc = Object.getOwnPropertyDescriptor(f, prop);
     var g_desc = Object.getOwnPropertyDescriptor(g, prop);
-    if (prop === "prototype") {
-      // ES6 draft 03-17-2015 section 25.2.2.2
-      assertFalse(g_desc.writable, prop);
-      assertFalse(g_desc.enumerable, prop);
-      assertFalse(g_desc.configurable, prop);
-    } else {
-      assertEquals(f_desc.configurable, g_desc.configurable, prop);
-      assertEquals(f_desc.writable, g_desc.writable, prop);
-      assertEquals(f_desc.enumerable, g_desc.enumerable, prop);
-    }
+    assertEquals(f_desc.configurable, g_desc.configurable, prop);
+    assertEquals(f_desc.writable, g_desc.writable, prop);
+    assertEquals(f_desc.enumerable, g_desc.enumerable, prop);
   }
 }
 TestGeneratorFunctionInstance();
 
 
 // Generators have an additional object interposed in the chain between
 // themselves and Function.prototype.
 function TestGeneratorFunctionPrototype() {
   // Sanity check.
   assertSame(Object.getPrototypeOf(f), Function.prototype);
@@ skipping 88 matching lines @@
 function TestPerGeneratorPrototype() {
   assertTrue((function*(){}).prototype !== (function*(){}).prototype);
   assertTrue((function*(){}).prototype !== g.prototype);
   assertSame(GeneratorObjectPrototype, Object.getPrototypeOf(g.prototype));
   assertTrue(!(g.prototype instanceof Function));
   assertSame(typeof (g.prototype), "object");
 
   assertArrayEquals([], Object.getOwnPropertyNames(g.prototype));
 }
 TestPerGeneratorPrototype();