Add CHECKs to make sure ThreadableLoader has not been created multiple times

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 650 matching lines @@
 }
 
 void WorkerThreadableLoader::MainThreadLoaderHolder::start(
     Document& document,
     std::unique_ptr<CrossThreadResourceRequestData> request,
     const ThreadableLoaderOptions& options,
     const ResourceLoaderOptions& originalResourceLoaderOptions) {
   DCHECK(isMainThread());
   ResourceLoaderOptions resourceLoaderOptions = originalResourceLoaderOptions;
   resourceLoaderOptions.requestInitiatorContext = WorkerContext;
+  // TODO(yhirano): Remove this CHECK once https://crbug.com/667254 is fixed.
+  CHECK(!m_mainThreadLoader);
   m_mainThreadLoader = DocumentThreadableLoader::create(document, this, options,
                                                         resourceLoaderOptions);
   m_mainThreadLoader->start(ResourceRequest(request.get()));
 }
 
 }  // namespace blink