Add initial link preload support

Source/core/html/LinkRelAttribute.cpp

 /*
  * Copyright (C) 2011 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 62 matching lines @@
             m_iconType = Favicon;
         } else if (equalIgnoringCase(linkType, "prefetch")) {
             m_isLinkPrefetch = true;
         } else if (equalIgnoringCase(linkType, "dns-prefetch")) {
             m_isDNSPrefetch = true;
         } else if (equalIgnoringCase(linkType, "preconnect")) {
             if (RuntimeEnabledFeatures::linkPreconnectEnabled())
                 m_isPreconnect = true;
         } else if (equalIgnoringCase(linkType, "subresource")) {
             m_isLinkSubresource = true;
+        } else if (equalIgnoringCase(linkType, "preload")) {
+            if (RuntimeEnabledFeatures::linkPreloadEnabled())
+                m_isLinkPreload = true;
         } else if (equalIgnoringCase(linkType, "prerender")) {
             m_isLinkPrerender = true;
         } else if (equalIgnoringCase(linkType, "next")) {
             m_isLinkNext = true;
         } else if (equalIgnoringCase(linkType, "apple-touch-icon")) {
             if (RuntimeEnabledFeatures::touchIconLoadingEnabled())
                 m_iconType = TouchIcon;
         } else if (equalIgnoringCase(linkType, "apple-touch-icon-precomposed")) {
             if (RuntimeEnabledFeatures::touchIconLoadingEnabled())
                 m_iconType = TouchPrecomposedIcon;
         } else if (equalIgnoringCase(linkType, "manifest")) {
             m_isManifest = true;
         } else if (equalIgnoringCase(rel, "transition-exiting-stylesheet")) {
             if (RuntimeEnabledFeatures::navigationTransitionsEnabled())
                 m_isTransitionExitingStylesheet = true;
         } else if (equalIgnoringCase(linkType, "default-presentation")) {
             if (RuntimeEnabledFeatures::presentationEnabled())
                 m_isDefaultPresentation = true;
         }
     }
 }
 
 }