Fix incorrect comment about XMLHttpRequest::handleDidCancel()

Source/core/xml/XMLHttpRequest.h

 /*
  *  Copyright (C) 2003, 2006, 2008 Apple Inc. All rights reserved.
  *  Copyright (C) 2005, 2006 Alexey Proskuryakov <ap@nypop.com>
  *  Copyright (C) 2011 Google Inc. All rights reserved.
  *  Copyright (C) 2012 Intel Corporation
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
  *  version 2 of the License, or (at your option) any later version.
@@ skipping 193 matching lines @@
     // Dispatches a response ProgressEvent.
     void dispatchProgressEvent(const AtomicString&, long long, long long);
     // Dispatches a response ProgressEvent using values sampled from
     // m_receivedLength and m_response.
     void dispatchProgressEventFromSnapshot(const AtomicString&);
 
     // Does clean up common for all kind of didFail() call.
     void handleDidFailGeneric();
     // Handles didFail() call not caused by cancellation or timeout.
     void handleNetworkError();
-    // Handles didFail() call triggered by m_loader->cancel().
+    // Handles didFail() call for cancellations. For example, the
+    // ResourceLoader handling the load notifies m_loader of an error
+    // cancellation when the frame containing the XHR navigates away.
     void handleDidCancel();
     // Handles didFail() call for timeout.
     void handleDidTimeout();
 
     void handleRequestError(ExceptionCode, const AtomicString&, long long, long long);
 
     OwnPtrWillBeMember<XMLHttpRequestUpload> m_upload;
 
     KURL m_url;
     AtomicString m_method;
@@ skipping 46 matching lines @@
     bool m_parsedResponse;
     bool m_error;
     bool m_uploadEventsAllowed;
     bool m_uploadComplete;
     bool m_sameOriginRequest;
 };
 
 } // namespace blink
 
 #endif // XMLHttpRequest_h