Allow XHR timeout attribute to be overridden after send(), per spec

Source/core/loader/ThreadableLoader.h

 /*
  * Copyright (C) 2009 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 110 matching lines @@
     public:
         // ThreadableLoaderOptions argument configures this ThreadableLoader's
         // behavior.
         //
         // ResourceLoaderOptions argument will be passed to the FetchRequest
         // that this ThreadableLoader creates. It can be altered e.g. when
         // redirect happens.
         static void loadResourceSynchronously(ExecutionContext&, const ResourceRequest&, ThreadableLoaderClient&, const ThreadableLoaderOptions&, const ResourceLoaderOptions&);
         static PassRefPtr<ThreadableLoader> create(ExecutionContext&, ThreadableLoaderClient*, const ResourceRequest&, const ThreadableLoaderOptions&, const ResourceLoaderOptions&);
 
+        // A ThreadableLoader may have a timeout specified. It is possible, in some cases, for
+        // the timeout to be overridden after the request is sent (for example, XMLHttpRequests
+        // may override their timeout setting after sending).
+        //
+        // Set a new timeout relative to the time the request started, in milliseconds.
+        virtual void overrideTimeout(unsigned long timeoutMilliseconds) = 0;
+
         virtual void cancel() = 0;
 
         virtual ~ThreadableLoader() { }
 
     protected:
         ThreadableLoader() { }
     };
 
 } // namespace blink
 
 #endif // ThreadableLoader_h