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..7a044d3b38cbc436483c63a070e366a2228bb7b8 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.
+    return Resource::Raw;

[Mike West, 2015/04/07 06:26:28]

Where is this used? Could we use request contexts instead?

I'm hoping we can get rid of `Resource::Type` at some point. CSP is the only
infrastructure I know of that's actively using it.

[Yoav Weiss, 2015/04/07 07:26:14]

It's used by ResourceFetcher to determine context and hence priority.
Currently it does nothing since I'm planning to add that in a followup CL.
Also, I think that I'd need to do some cleanup and decouple request priority
from context, since as currently defined `as` does not determine context, but
does determine the request priority.

[Mike West, 2015/04/07 12:23:01]

Hrm. Ok. That seems strange. I wouldn't block you from landing this, but I'd
suggest that thinking about those interactions might be reasonable.

+}
+
+void LinkLoader::preloadIfNeeded(const LinkRelAttribute& relAttribute, const KURL& href, Document& document, const String& as)
+{

[Mike West, 2015/04/07 06:26:28]

ASSERT that the runtime flag is enabled?

[Yoav Weiss, 2015/04/07 07:26:14]

There's one a few lines below. I'll bump it up for better visibility.

[Mike West, 2015/04/07 12:23:01]

You're right, sorry. My eyes are obviously broken.

+    if (relAttribute.isLinkPreload() && href.isValid()) {
+        FetchRequest linkRequest(ResourceRequest(document.completeURL(href)), FetchInitiatorTypeNames::link);
+        Resource::Type type = getTypeFromAsAttribute(as);
+        ASSERT(RuntimeEnabledFeatures::linkPreloadEnabled());
+        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())