Fix Object.prototype.toString() when @@toStringTag is not a string.

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index c2f6a40ef3d75b24aa1b35a57f91436cca08c7d2..7b6270745bad9a3b09d28aebb836d8dcb65fddca 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -1135,6 +1135,10 @@ Local<ObjectTemplate> Shell::CreateGlobalTemplate(Isolate* isolate) {
       String::NewFromUtf8(isolate, "version", NewStringType::kNormal)
           .ToLocalChecked(),
       FunctionTemplate::New(isolate, Version));
+  global_template->Set(
+      Symbol::GetToStringTag(isolate),
+      String::NewFromUtf8(isolate, "global", NewStringType::kNormal)
+          .ToLocalChecked());
 
   // Bind the Realm object.
   Local<ObjectTemplate> realm_template = ObjectTemplate::New(isolate);