Add initial link preload support

Source/core/loader/LinkLoader.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 120 matching lines @@
 static void preconnectIfNeeded(const LinkRelAttribute& relAttribute, const KURL& href, Document& document)
 {
     if (relAttribute.isPreconnect() && href.isValid()) {
         ASSERT(RuntimeEnabledFeatures::linkPreconnectEnabled());
         if (document.settings()->logDnsPrefetchAndPreconnect())
             document.addConsoleMessage(ConsoleMessage::create(OtherMessageSource, DebugMessageLevel, String("Preconnect triggered for " + href.host())));
         preconnect(href);
     }
 }
 
+// TODO(yoav): Replace Resource:Type here with some way that conveys priority but not context.
+static bool getTypeFromAsAttribute(const String& as, Resource::Type& type)
+{
+    if (as.isEmpty())
+        return false;
+    // TODO(yoav): Return false also when the `as` value is not a valid one.
+    // TODO(yoav): Add actual types here and make sure priorities work accordingly.
+    type = Resource::Raw;
+    return true;
+}
+
+void LinkLoader::preloadIfNeeded(const LinkRelAttribute& relAttribute, const KURL& href, Document& document, const String& as)
+{
+    if (relAttribute.isLinkPreload()) {
+        ASSERT(RuntimeEnabledFeatures::linkPreloadEnabled());
+        if (!href.isValid() || href.isEmpty()) {
+            document.addConsoleMessage(ConsoleMessage::create(OtherMessageSource, WarningMessageLevel, String("<link rel=preload> has an invalid `href` value")));
+            return;
+        }
+        Resource::Type type;
+        if (!getTypeFromAsAttribute(as, type)) {
+            document.addConsoleMessage(ConsoleMessage::create(OtherMessageSource, WarningMessageLevel, String("<link rel=preload> must have a valid `as` value")));
+            return;
+        }
+        FetchRequest linkRequest(ResourceRequest(document.completeURL(href)), FetchInitiatorTypeNames::link);
+        if (document.settings()->logPreload())
+            document.addConsoleMessage(ConsoleMessage::create(OtherMessageSource, DebugMessageLevel, String("Preload triggered for " + href.host() + href.path())));
+        setResource(document.fetcher()->fetchLinkPreloadResource(type, linkRequest));
+    }
+}
+
 bool LinkLoader::loadLinkFromHeader(const String& headerValue, Document* document)
 {
     if (!document)
         return false;
     LinkHeaderSet headerSet(headerValue);
     for (auto& header : headerSet) {
         if (!header.valid() || header.url().isEmpty() || header.rel().isEmpty())
             return false;
         LinkRelAttribute relAttribute(header.rel());
         KURL url = document->completeURL(header.url());
         if (RuntimeEnabledFeatures::linkHeaderEnabled())
             dnsPrefetchIfNeeded(relAttribute, url, *document);
 
         if (RuntimeEnabledFeatures::linkPreconnectEnabled())
             preconnectIfNeeded(relAttribute, url, *document);
 
         // FIXME: Add more supported headers as needed.
     }
     return true;
 }
 
-bool LinkLoader::loadLink(const LinkRelAttribute& relAttribute, const AtomicString& crossOriginMode, const String& type, const KURL& href, Document& document)
+bool LinkLoader::loadLink(const LinkRelAttribute& relAttribute, const AtomicString& crossOriginMode, const String& type, const String& as, const KURL& href, Document& document)
 {
+    // FIXME(crbug.com/463266): We're ignoring type here. Maybe we shouldn't.
     dnsPrefetchIfNeeded(relAttribute, href, document);
 
     preconnectIfNeeded(relAttribute, href, document);
 
+    preloadIfNeeded(relAttribute, href, document, as);
+
     // FIXME(crbug.com/323096): Should take care of import.
     if ((relAttribute.isLinkPrefetch() || relAttribute.isLinkSubresource() || relAttribute.isTransitionExitingStylesheet()) && href.isValid() && document.frame()) {
         if (!m_client->shouldLoadLink())
             return false;
         Resource::Type type = relAttribute.isLinkSubresource() ?  Resource::LinkSubresource : Resource::LinkPrefetch;
         FetchRequest linkRequest(ResourceRequest(document.completeURL(href)), FetchInitiatorTypeNames::link);
         if (!crossOriginMode.isNull())
             linkRequest.setCrossOriginAccessControl(document.securityOrigin(), crossOriginMode);
         setResource(document.fetcher()->fetchLinkResource(type, linkRequest));
     }
@@ skipping 22 matching lines @@
         m_prerender.clear();
     }
 }
 
 DEFINE_TRACE(LinkLoader)
 {
     visitor->trace(m_prerender);
 }
 
 }