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

third_party/WebKit/Source/modules/fetch/FetchManager.cpp

 // Copyright 2014 The Chromium 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 "modules/fetch/FetchManager.h"
 
 #include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "bindings/core/v8/ScriptState.h"
 #include "bindings/core/v8/V8ThrowException.h"
@@ skipping 820 matching lines @@
       threadableLoaderOptions.crossOriginRequestPolicy = UseAccessControl;
       break;
     case WebURLRequest::FetchRequestModeNavigate:
       // Using DenyCrossOriginRequests here to reduce the security risk.
       // "navigate" request is only available in ServiceWorker.
       threadableLoaderOptions.crossOriginRequestPolicy =
           DenyCrossOriginRequests;
       break;
   }
   InspectorInstrumentation::willStartFetch(m_executionContext, this);
+  // TODO(yhirano): Remove this CHECK once https://crbug.com/667254 is fixed.
+  CHECK(!m_loader);
   m_loader =
       ThreadableLoader::create(*m_executionContext, this,
                                threadableLoaderOptions, resourceLoaderOptions);
   m_loader->start(request);
 }
 
 // performDataFetch() is almost the same as performHTTPFetch(), except for:
 // - We set AllowCrossOriginRequests to allow requests to data: URLs in
 //   'same-origin' mode.
 // - We reject non-GET method.
@@ skipping 81 matching lines @@
   m_loaders.remove(loader);
   loader->dispose();
 }
 
 DEFINE_TRACE(FetchManager) {
   visitor->trace(m_loaders);
   ContextLifecycleObserver::trace(visitor);
 }
 
 }  // namespace blink