Properly disable ES6 generator support for TurboFan.

src/generator.js

 // Copyright 2013 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.
 
 "use strict";
 
 // This file relies on the fact that the following declarations have been made
 // in runtime.js:
 // var $Function = global.Function;
 
@@ skipping 39 matching lines @@
   var f = %CompileString(source, true);
   if (!IS_FUNCTION(f)) return f;
   f = %_CallFunction(global_proxy, f);
   %FunctionMarkNameShouldPrintAsAnonymous(f);
   return f;
 }
 
 
 function SetUpGenerators() {
   %CheckIsBootstrapping();
+
+  // Both Runtime_GeneratorNext and Runtime_GeneratorThrow are supported by
+  // neither Crankshaft nor TurboFan, disable optimization of wrappers here.
+  %NeverOptimizeFunction(GeneratorObjectNext);
+  %NeverOptimizeFunction(GeneratorObjectThrow);
+
+  // Set up non-enumerable functions on the generator prototype object.
   var GeneratorObjectPrototype = GeneratorFunctionPrototype.prototype;
   InstallFunctions(GeneratorObjectPrototype,
                    DONT_ENUM | DONT_DELETE | READ_ONLY,
                    ["next", GeneratorObjectNext,
                     "throw", GeneratorObjectThrow]);
+
   %FunctionSetName(GeneratorObjectIterator, '[Symbol.iterator]');
   %AddNamedProperty(GeneratorObjectPrototype, symbolIterator,
       GeneratorObjectIterator, DONT_ENUM | DONT_DELETE | READ_ONLY);
   %AddNamedProperty(GeneratorObjectPrototype, "constructor",
       GeneratorFunctionPrototype, DONT_ENUM | DONT_DELETE | READ_ONLY);
   %InternalSetPrototype(GeneratorFunctionPrototype, $Function.prototype);
   %SetCode(GeneratorFunctionPrototype, GeneratorFunctionPrototypeConstructor);
   %AddNamedProperty(GeneratorFunctionPrototype, "constructor",
       GeneratorFunction, DONT_ENUM | DONT_DELETE | READ_ONLY);
   %InternalSetPrototype(GeneratorFunction, $Function);
   %SetCode(GeneratorFunction, GeneratorFunctionConstructor);
 }
 
 SetUpGenerators();