[generators] Implement Generator.prototype.return.

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 81 matching lines @@
 
 
 // Functions that we associate with generator objects are actually defined by
 // a common prototype.
 function TestGeneratorObjectPrototype() {
   assertSame(IteratorPrototype,
              Object.getPrototypeOf(GeneratorObjectPrototype));
   assertSame(GeneratorObjectPrototype,
              Object.getPrototypeOf((function*(){yield 1}).prototype));
 
-  var expected_property_names = ["next", "throw", "constructor"];
+  var expected_property_names = ["next", "return", "throw", "constructor"];
   var found_property_names =
       Object.getOwnPropertyNames(GeneratorObjectPrototype);
 
   expected_property_names.sort();
   found_property_names.sort();
 
   assertArrayEquals(expected_property_names, found_property_names);
 
   var constructor_desc = Object.getOwnPropertyDescriptor(
       GeneratorObjectPrototype, "constructor");
@@ skipping 50 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();