Use instance type in Object::IsErrorObject().

src/messages.cc

 // Copyright 2011 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/messages.h"
 
 #include "src/api.h"
 #include "src/execution.h"
 #include "src/isolate-inl.h"
 #include "src/keys.h"
@@ skipping 80 matching lines @@
   isolate->set_external_caught_exception(false);
 
   // Turn the exception on the message into a string if it is an object.
   if (message->argument()->IsJSObject()) {
     HandleScope scope(isolate);
     Handle<Object> argument(message->argument(), isolate);
 
     MaybeHandle<Object> maybe_stringified;
     Handle<Object> stringified;
     // Make sure we don't leak uncaught internally generated Error objects.
-    if (Object::IsErrorObject(isolate, argument)) {
+    if (argument->IsJSError()) {
       Handle<Object> args[] = {argument};
       maybe_stringified = Execution::TryCall(
           isolate, isolate->no_side_effects_to_string_fun(),
           isolate->factory()->undefined_value(), arraysize(args), args);
     } else {
       v8::TryCatch catcher(reinterpret_cast<v8::Isolate*>(isolate));
       catcher.SetVerbose(false);
       catcher.SetCaptureMessage(false);
 
       maybe_stringified = Object::ToString(isolate, argument);
@@ skipping 327 matching lines @@
       builder.AppendCharacter(*c);
     }
   }
 
   return builder.Finish();
 }
 
 
 }  // namespace internal
 }  // namespace v8