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

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 42f16d8ff0fec61240ddb7dd70c30ffb2d1dc2aa..66b12ead9e7a912c0ee3defe7392d2557f20a926 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -1318,8 +1318,19 @@ Handle<JSFunction> Factory::NewFunctionFromSharedFunctionInfo(
     PretenureFlag pretenure) {
   int map_index =
       Context::FunctionMapIndex(info->language_mode(), info->kind());
-  Handle<Map> map(Map::cast(context->native_context()->get(map_index)));
-  Handle<JSFunction> result = NewFunction(map, info, context, pretenure);
+  Handle<Map> initial_map(Map::cast(context->native_context()->get(map_index)));
+
+  return NewFunctionFromSharedFunctionInfo(initial_map, info, context,
+                                           pretenure);
+}
+
+
+Handle<JSFunction> Factory::NewFunctionFromSharedFunctionInfo(
+    Handle<Map> initial_map, Handle<SharedFunctionInfo> info,
+    Handle<Context> context, PretenureFlag pretenure) {
+  DCHECK_EQ(JS_FUNCTION_TYPE, initial_map->instance_type());
+  Handle<JSFunction> result =
+      NewFunction(initial_map, info, context, pretenure);
 
   if (info->ic_age() != isolate()->heap()->global_ic_age()) {
     info->ResetForNewContext(isolate()->heap()->global_ic_age());