Add initial link preload support

Source/core/html/LinkRelAttribute.cpp

Index: Source/core/html/LinkRelAttribute.cpp
diff --git a/Source/core/html/LinkRelAttribute.cpp b/Source/core/html/LinkRelAttribute.cpp
index 66588e58da753542f5badb53e486f059146b6191..8df7495f47c60d03e61d771c710d03b0e9bef701 100644
--- a/Source/core/html/LinkRelAttribute.cpp
+++ b/Source/core/html/LinkRelAttribute.cpp
@@ -44,6 +44,7 @@ LinkRelAttribute::LinkRelAttribute(const String& rel)
     , m_isPreconnect(false)
     , m_isLinkPrefetch(false)
     , m_isLinkSubresource(false)
+    , m_isLinkPreload(false)
     , m_isLinkPrerender(false)
     , m_isLinkNext(false)
     , m_isImport(false)
@@ -80,6 +81,9 @@ LinkRelAttribute::LinkRelAttribute(const String& rel)
                 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")) {