Make generators non-constructable.

test/mjsunit/es6/generators-objects.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 41 matching lines @@
 function TestGeneratorObject() {
   function* g() { yield 1; }
 
   var iter = g();
   assertSame(g.prototype, Object.getPrototypeOf(iter));
   assertTrue(iter instanceof g);
   assertEquals("Generator", %_ClassOf(iter));
   assertEquals("[object Generator]", String(iter));
   assertEquals([], Object.getOwnPropertyNames(iter));
   assertTrue(iter !== g());
-
-  // g() is the same as new g().
-  iter = new g();
-  assertSame(g.prototype, Object.getPrototypeOf(iter));
-  assertTrue(iter instanceof g);
-  assertEquals("Generator", %_ClassOf(iter));
-  assertEquals("[object Generator]", String(iter));
   assertEquals("[object Generator]", Object.prototype.toString.call(iter));
   var gf = iter.__proto__.constructor;
   assertEquals("[object GeneratorFunction]", Object.prototype.toString.call(gf));
-  assertEquals([], Object.getOwnPropertyNames(iter));
-  assertTrue(iter !== new g());
+
+  // generators are not constructable.
+  assertThrows(()=>new g());
 }
 TestGeneratorObject();
 
 
 // Test the methods of generator objects.
 function TestGeneratorObjectMethods() {
   function* g() { yield 1; }
   var iter = g();
 
   function TestNonGenerator(non_generator) {
     assertThrows(function() { iter.next.call(non_generator); }, TypeError);
     assertThrows(function() { iter.next.call(non_generator, 1); }, TypeError);
     assertThrows(function() { iter.throw.call(non_generator, 1); }, TypeError);
   }
 
   TestNonGenerator(1);
   TestNonGenerator({});
   TestNonGenerator(function(){});
   TestNonGenerator(g);
   TestNonGenerator(g.prototype);
 }
 TestGeneratorObjectMethods();