Add initial link preload support

Source/core/loader/LinkLoader.cpp

Index: Source/core/loader/LinkLoader.cpp
diff --git a/Source/core/loader/LinkLoader.cpp b/Source/core/loader/LinkLoader.cpp
index d7156b9dc29836fce698f50953e188e1b466d959..28950e21748839503b6302807f3b56107b596a5c 100644
--- a/Source/core/loader/LinkLoader.cpp
+++ b/Source/core/loader/LinkLoader.cpp
@@ -138,6 +138,24 @@ static void preconnectIfNeeded(const LinkRelAttribute& relAttribute, const KURL&
     }
 }
 
+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)
@@ -159,12 +177,15 @@ bool LinkLoader::loadLinkFromHeader(const String& headerValue, Document* documen
     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())