[stubs] Introduce NonPrimitiveToPrimitive builtin.

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 347ed38db28db5fda8b1a5f48d3e33ec23b94454..1208de275b52f549f82db378ac29d717e16565af 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -2382,6 +2382,18 @@ 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