Properly disable ES6 generator support for TurboFan.

src/generator.js

Index: src/generator.js
diff --git a/src/generator.js b/src/generator.js
index c62fe2c771389db255528087262c9ead49d55b39..c94c4ff0db1d1fe59e9bdbd932e935e69a1d2d91 100644
--- a/src/generator.js
+++ b/src/generator.js
@@ -57,11 +57,19 @@ function GeneratorFunctionConstructor(arg1) {  // length == 1
 
 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);