Make the error message in WorkerThreadableLoader more developer-friendly.

third_party/WebKit/Source/core/loader/WorkerThreadableLoader.cpp

 /*
  * Copyright (C) 2009, 2010 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 129 matching lines @@
     ASSERT(isMainThread());
     Document* document = toDocument(context);
 
     ResourceRequest request(requestData.get());
     if (!request.didSetHTTPReferrer())
         request.setHTTPReferrer(SecurityPolicy::generateReferrer(referrerPolicy, request.url(), outgoingReferrer));
     resourceLoaderOptions.requestInitiatorContext = WorkerContext;
     m_mainThreadLoader = DocumentThreadableLoader::create(*document, this, request, options, resourceLoaderOptions);
     if (!m_mainThreadLoader) {
         // DocumentThreadableLoader::create may return 0 when the document loader has been already changed.
-        didFail(ResourceError(errorDomainBlinkInternal, 0, request.url().string(), "Can't create DocumentThreadableLoader"));
+        didFail(ResourceError(errorDomainBlinkInternal, 0, request.url().string(), "The parent document page has been unloaded."));
     }
 }
 
 void WorkerThreadableLoader::MainThreadBridge::mainThreadDestroy(ExecutionContext* context)
 {
     ASSERT(isMainThread());
     ASSERT_UNUSED(context, context->isDocument());
     delete this;
 }
 
@@ skipping 104 matching lines @@
 {
     m_clientBridge->didFailRedirectCheck();
 }
 
 void WorkerThreadableLoader::MainThreadBridge::didReceiveResourceTiming(const ResourceTimingInfo& info)
 {
     m_clientBridge->didReceiveResourceTiming(info);
 }
 
 } // namespace blink