[es6] Introduce spec compliant IsConstructor.

src/runtime/runtime-function.cc

Index: src/runtime/runtime-function.cc
diff --git a/src/runtime/runtime-function.cc b/src/runtime/runtime-function.cc
index 560016659d6a6cf9998f7b2fd088a365f5eb415e..be92d59a64ea9ae8ba62999eb8f0c1796335d452 100644
--- a/src/runtime/runtime-function.cc
+++ b/src/runtime/runtime-function.cc
@@ -159,7 +159,7 @@ RUNTIME_FUNCTION(Runtime_FunctionSetPrototype) {
 
   CONVERT_ARG_HANDLE_CHECKED(JSFunction, fun, 0);
   CONVERT_ARG_HANDLE_CHECKED(Object, value, 1);
-  RUNTIME_ASSERT(fun->should_have_prototype());
+  RUNTIME_ASSERT(fun->IsConstructor());
   RETURN_FAILURE_ON_EXCEPTION(isolate,
                               Accessors::FunctionSetPrototype(fun, value));
   return args[0];  // return TOS
@@ -270,30 +270,10 @@ RUNTIME_FUNCTION(Runtime_SetNativeFlag) {
 
 
 RUNTIME_FUNCTION(Runtime_IsConstructor) {
-  HandleScope handles(isolate);
-  RUNTIME_ASSERT(args.length() == 1);
-
-  CONVERT_ARG_HANDLE_CHECKED(Object, object, 0);
-
-  // TODO(caitp): implement this in a better/simpler way, allow inlining via TF
-  if (object->IsJSFunction()) {
-    Handle<JSFunction> func = Handle<JSFunction>::cast(object);
-    bool should_have_prototype = func->should_have_prototype();
-    if (func->shared()->bound()) {
-      Handle<FixedArray> bound_args =
-          Handle<FixedArray>(FixedArray::cast(func->function_bindings()));
-      Handle<Object> bound_function(
-          JSReceiver::cast(bound_args->get(JSFunction::kBoundFunctionIndex)),
-          isolate);
-      if (bound_function->IsJSFunction()) {
-        Handle<JSFunction> bound = Handle<JSFunction>::cast(bound_function);
-        DCHECK(!bound->shared()->bound());
-        should_have_prototype = bound->should_have_prototype();
-      }
-    }
-    return isolate->heap()->ToBoolean(should_have_prototype);
-  }
-  return isolate->heap()->false_value();
+  SealHandleScope shs(isolate);
+  DCHECK_EQ(1, args.length());
+  CONVERT_ARG_CHECKED(Object, object, 0);
+  return isolate->heap()->ToBoolean(object->IsConstructor());
 }
 
 
@@ -437,6 +417,10 @@ RUNTIME_FUNCTION(Runtime_FunctionBindArguments) {
     bound_function_map = Map::TransitionToPrototype(bound_function_map, proto,
                                                     REGULAR_PROTOTYPE);
   }
+  if (bound_function_map->is_constructor() != bindee->IsConstructor()) {
+    bound_function_map = Map::Copy(bound_function_map, "IsConstructor");
+    bound_function_map->set_is_constructor(bindee->IsConstructor());
+  }
   JSObject::MigrateToMap(bound_function, bound_function_map);
 
   Handle<String> length_string = isolate->factory()->length_string();