Add initial link preload support

Source/core/html/HTMLLinkElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 113 matching lines @@
 class HTMLLinkElement final : public HTMLElement, public LinkLoaderClient {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static PassRefPtrWillBeRawPtr<HTMLLinkElement> create(Document&, bool createdByParser);
     virtual ~HTMLLinkElement();
 
     KURL href() const;
     const AtomicString& rel() const;
     String media() const { return m_media; }
     String typeValue() const { return m_type; }
+    String asValue() const { return m_as; }
     const LinkRelAttribute& relAttribute() const { return m_relAttribute; }
 
     const AtomicString& type() const;
 
     IconType iconType() const;
 
     // the icon sizes as parsed from the HTML attribute
     const Vector<IntSize>& iconSizes() const;
 
     bool async() const;
@@ skipping 12 matching lines @@
 
     void dispatchPendingEvent(LinkEventSender*);
     void scheduleEvent();
     void dispatchEventImmediately();
     static void dispatchPendingLoadEvents();
 
     // From LinkLoaderClient
     virtual bool shouldLoadLink() override;
 
     // For LinkStyle
-    bool loadLink(const String& type, const KURL&);
+    bool loadLink(const String& type, const String& as, const KURL&);
     bool isAlternate() const { return linkStyle()->isUnset() && m_relAttribute.isAlternate(); }
     bool shouldProcessStyle() { return linkResourceToProcess() && linkStyle(); }
     bool isCreatedByParser() const { return m_createdByParser; }
 
     // Parse the icon size attribute into |iconSizes|, make this method public
     // visible for testing purpose.
     static void parseSizesAttribute(const AtomicString& value, Vector<IntSize>& iconSizes);
 
     DECLARE_VIRTUAL_TRACE();
 
@@ skipping 27 matching lines @@
     virtual void didSendLoadForLinkPrerender() override;
     virtual void didSendDOMContentLoadedForLinkPrerender() override;
 
 private:
     HTMLLinkElement(Document&, bool createdByParser);
 
     OwnPtrWillBeMember<LinkResource> m_link;
     LinkLoader m_linkLoader;
 
     String m_type;
+    String m_as;
     String m_media;
     RefPtrWillBeMember<DOMSettableTokenList> m_sizes;
     Vector<IntSize> m_iconSizes;
     LinkRelAttribute m_relAttribute;
 
     bool m_createdByParser;
     bool m_isInShadowTree;
 };
 
 } // namespace blink
 
 #endif // HTMLLinkElement_h