CORS: Handle error HTTP status code 4XX/5XX in preflight requests.

Source/core/loader/DocumentThreadableLoader.cpp

Index: Source/core/loader/DocumentThreadableLoader.cpp
diff --git a/Source/core/loader/DocumentThreadableLoader.cpp b/Source/core/loader/DocumentThreadableLoader.cpp
index 2787d98be9b4a1308929ac2138fa9ef60857244f..5471fdb5f057992e9d29cf3ec8990f1026593ac6 100644
--- a/Source/core/loader/DocumentThreadableLoader.cpp
+++ b/Source/core/loader/DocumentThreadableLoader.cpp
@@ -286,6 +286,11 @@ void DocumentThreadableLoader::didReceiveResponse(unsigned long identifier, cons
             return;
         }
 
+        if (!passesPreflightStatusCheck(response, accessControlErrorDescription)) {
+            preflightFailure(identifier, response.url().string(), accessControlErrorDescription);
+            return;
+        }
+
         OwnPtr<CrossOriginPreflightResultCacheItem> preflightResult = adoptPtr(new CrossOriginPreflightResultCacheItem(m_options.allowCredentials));
         if (!preflightResult->parse(response, accessControlErrorDescription)
             || !preflightResult->allowsCrossOriginMethod(m_actualRequest->httpMethod(), accessControlErrorDescription)