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

Source/core/loader/ThreadableLoader.h

Index: Source/core/loader/ThreadableLoader.h
diff --git a/Source/core/loader/ThreadableLoader.h b/Source/core/loader/ThreadableLoader.h
index b0f008523d3c27e692eb902a4026d065a7d28f22..f0eddc612935de9eeb0cf0c4d29563acfa632603 100644
--- a/Source/core/loader/ThreadableLoader.h
+++ b/Source/core/loader/ThreadableLoader.h
@@ -128,6 +128,13 @@ namespace blink {
         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() { }