Gracefully handle backdoor cancellations of synchronous resource fetches.

Source/core/fetch/ResourceLoader.cpp

 /*
  * Copyright (C) 2006, 2007, 2010, 2011 Apple Inc. All rights reserved.
  *           (C) 2007 Graham Dennis (graham.dennis@gmail.com)
  *
  * 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.
@@ skipping 495 matching lines @@
     RELEASE_ASSERT(m_connectionState == ConnectionStateNew);
     m_connectionState = ConnectionStateStarted;
 
     WrappedResourceRequest requestIn(m_request);
     WebURLResponse responseOut;
     responseOut.initialize();
     WebURLError errorOut;
     WebData dataOut;
     loader->loadSynchronously(requestIn, responseOut, errorOut, dataOut);
     if (errorOut.reason) {
+        if (m_state == Terminated) {
+            // A message dispatched while synchronously fetching the resource
+            // can bring about the cancellation of this load.
+            ASSERT(!m_resource);
+            return;
+        }
         didFail(0, errorOut);
         return;
     }
     didReceiveResponse(0, responseOut);
     if (m_state == Terminated)
         return;
     RefPtr<ResourceLoadInfo> resourceLoadInfo = responseOut.toResourceResponse().resourceLoadInfo();
     int64_t encodedDataLength = resourceLoadInfo ? resourceLoadInfo->encodedDataLength : WebURLLoaderClient::kUnknownEncodedDataLength;
     m_host->didReceiveData(m_resource, dataOut.data(), dataOut.size(), encodedDataLength);
     m_resource->setResourceBuffer(dataOut);
     didFinishLoading(0, monotonicallyIncreasingTime(), encodedDataLength);
 }
 
 ResourceRequest& ResourceLoader::applyOptions(ResourceRequest& request) const
 {
     request.setAllowStoredCredentials(m_options.allowCredentials == AllowStoredCredentials);
     return request;
 }
 
 }