Prevent entering XHR methods while loader is being cancelled.

Source/core/xml/XMLHttpRequest.idl

 /*
  * Copyright (C) 2008, 2011 Apple 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 46 matching lines @@
     readonly attribute unsigned short readyState;
 
     [SetterRaisesException] attribute boolean withCredentials;
 
     [Custom, ActivityLog=Access, RaisesException] void open(DOMString method, DOMString url, optional boolean async, optional DOMString user, optional DOMString password);
 
     [ActivityLog=Access, RaisesException] void setRequestHeader(DOMString header, DOMString value);
 
     [Custom, RaisesException] void send();
 
-    void abort();
+    [RaisesException] void abort();
 
     readonly attribute XMLHttpRequestUpload upload;
 
     // response
     [TreatReturnedNullStringAs=Undefined, RaisesException] DOMString getAllResponseHeaders();
     [TreatReturnedNullStringAs=Null, RaisesException] DOMString getResponseHeader(DOMString header);
     [CustomGetter, GetterRaisesException] readonly attribute DOMString responseText; // The custom getter implements TreatReturnedNullStringAs=Null
     [GetterRaisesException] readonly attribute Document responseXML;
 
     [SetterRaisesException] attribute XMLHttpRequestResponseType responseType;
     [CustomGetter, GetterRaisesException] readonly attribute Object response;
 
     [GetterRaisesException] readonly attribute unsigned short status;
     [GetterRaisesException] readonly attribute DOMString statusText;
 
     // Extension
     void overrideMimeType(DOMString override);
 };