Add initial link preload support

Source/core/html/HTMLLinkElement.h

Index: Source/core/html/HTMLLinkElement.h
diff --git a/Source/core/html/HTMLLinkElement.h b/Source/core/html/HTMLLinkElement.h
index bd5e61c4461cc28ec704fd6fa5cbc6cb8630fcfd..a0fd1cd3c53d0f88437449469f387d0602e7343a 100644
--- a/Source/core/html/HTMLLinkElement.h
+++ b/Source/core/html/HTMLLinkElement.h
@@ -131,6 +131,7 @@ public:
     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;
@@ -163,7 +164,7 @@ public:
     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; }
@@ -211,6 +212,7 @@ private:
     LinkLoader m_linkLoader;
 
     String m_type;
+    String m_as;
     String m_media;
     RefPtrWillBeMember<DOMSettableTokenList> m_sizes;
     Vector<IntSize> m_iconSizes;