[stubs] Introduce NonPrimitiveToPrimitive builtin.

src/factory.cc

 // Copyright 2014 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.
 
 #include "src/factory.h"
 
 #include "src/allocation-site-scopes.h"
 #include "src/base/bits.h"
 #include "src/bootstrapper.h"
 #include "src/conversions.h"
@@ skipping 2364 matching lines @@
   if (Name::Equals(name, nan_string())) return nan_value();
   if (Name::Equals(name, infinity_string())) return infinity_value();
   return Handle<Object>::null();
 }
 
 
 Handle<Object> Factory::ToBoolean(bool value) {
   return value ? true_value() : false_value();
 }
 
+Handle<String> Factory::ToPrimitiveHintString(ToPrimitiveHint hint) {
+  switch (hint) {
+    case ToPrimitiveHint::kDefault:
+      return default_string();
+    case ToPrimitiveHint::kNumber:
+      return number_string();
+    case ToPrimitiveHint::kString:
+      return string_string();
+  }
+  UNREACHABLE();
+  return Handle<String>::null();
+}
 
 }  // namespace internal
 }  // namespace v8