[es6] Fix Function and GeneratorFunction built-ins subclassing.

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index a8d0299095cb621cba2dbd3f2aff37ce51e76071..b023fea8502456bcb42ab5dab282c8b75425a511 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -1116,6 +1116,7 @@ void Genesis::InitializeGlobal(Handle<GlobalObject> global_object,
       InstallFunction(global, "Function", JS_FUNCTION_TYPE, JSFunction::kSize,
                       empty_function, Builtins::kIllegal);
   function_function->initial_map()->set_is_callable();
+  function_function->initial_map()->set_is_constructor(true);
 
   {  // --- A r r a y ---
     Handle<JSFunction> array_function =
@@ -1951,6 +1952,7 @@ void Bootstrapper::ExportFromRuntime(Isolate* isolate,
                         JSFunction::kSize, generator_function_prototype,
                         Builtins::kIllegal, kUseStrictFunctionMap);
     generator_function_function->initial_map()->set_is_callable();
+    generator_function_function->initial_map()->set_is_constructor(true);
   }
 
   {  // -- S e t I t e r a t o r