Say that the cause is preflight when CORS fails on invalid status code on preflight

Source/core/fetch/CrossOriginAccessControl.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 164 matching lines @@
 
 bool passesPreflightStatusCheck(const ResourceResponse& response, String& errorDescription)
 {
     // CORS preflight with 3XX is considered network error in
     // Fetch API Spec:
     //   https://fetch.spec.whatwg.org/#cors-preflight-fetch
     // CORS Spec:
     //   http://www.w3.org/TR/cors/#cross-origin-request-with-preflight-0
     // https://crbug.com/452394
     if (response.httpStatusCode() < 200 || response.httpStatusCode() >= 300) {
-        errorDescription = "Invalid HTTP status code " + String::number(response.httpStatusCode());
+        errorDescription = "Response for preflight has invalid HTTP status code " + String::number(response.httpStatusCode());
         return false;
     }
 
     return true;
 }
 
 void parseAccessControlExposeHeadersAllowList(const String& headerValue, HTTPHeaderSet& headerSet)
 {
     Vector<String> headers;
     headerValue.split(',', false, headers);
@@ skipping 60 matching lines @@
         request.setHTTPOrigin(securityOrigin->toAtomicString());
         // If the user didn't request credentials in the first place, update our
         // state so we neither request them nor expect they must be allowed.
         if (options.credentialsRequested == ClientDidNotRequestCredentials)
             options.allowCredentials = DoNotAllowStoredCredentials;
     }
     return true;
 }
 
 } // namespace blink