Add support for rel=next to Prerender in Blink.

Source/platform/exported/WebPrerender.cpp

 /*
  * Copyright (C) 2012 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 71 matching lines @@
     return m_private.isNull();
 }
 
 WebURL WebPrerender::url() const
 {
     return WebURL(m_private->url());
 }
 
 unsigned WebPrerender::relTypes() const
 {
-    // For now, all prerenders have RelTypePrerender.
-    // TODO: Once https://codereview.chromium.org/113803003/ lands in Chrome, re-land r164241 to set this correctly.
-    return PrerenderRelTypePrerender;
+    return m_private->relTypes();
 }
 
 WebString WebPrerender::referrer() const
 {
     return m_private->referrer();
 }
 
 WebReferrerPolicy WebPrerender::referrerPolicy() const
 {
     return static_cast<WebReferrerPolicy>(m_private->referrerPolicy());
@@ skipping 26 matching lines @@
 {
     m_private->didSendLoadForPrerender();
 }
 
 void WebPrerender::didSendDOMContentLoadedForPrerender()
 {
     m_private->didSendDOMContentLoadedForPrerender();
 }
 
 } // namespace blink