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);
     }
 }
 
+Resource::Type getTypeFromAsAttribute(const String& as)
+{
+    // FIXME: Add actual types here and make sure priorities work accordingly.

[Mike West, 2015/04/07 19:56:18]

Nit: We spell this `TODO(yoav):` now...

+    return Resource::Raw;
+}
+
+void LinkLoader::preloadIfNeeded(const LinkRelAttribute& relAttribute, const KURL& href, Document& document, const String& as)
+{
+    if (relAttribute.isLinkPreload() && href.isValid()) {

[Mike West, 2015/04/07 19:56:18]

https://w3c.github.io/preload/#fetch-settings says that `as` is mandatory; that
doesn't seem to be part of this patch. Is it intentionally not part of this
patch?

If you're planning to add it later, would you mind updating the CL description?

+        ASSERT(RuntimeEnabledFeatures::linkPreloadEnabled());
+        FetchRequest linkRequest(ResourceRequest(document.completeURL(href)), FetchInitiatorTypeNames::link);
+        Resource::Type type = getTypeFromAsAttribute(as);
+        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);
 }
 
 }