Added <link rel=preconnect> crossorigin attribute

Source/platform/network/NetworkHints.cpp

Index: Source/platform/network/NetworkHints.cpp
diff --git a/Source/platform/network/NetworkHints.cpp b/Source/platform/network/NetworkHints.cpp
index e48f51b48529fbbb7c93bedb8dc92e2a16716fc2..415b7082919f4c48bda63fc7ac6e1b5fd733ca72 100644
--- a/Source/platform/network/NetworkHints.cpp
+++ b/Source/platform/network/NetworkHints.cpp
@@ -38,8 +38,9 @@ void prefetchDNS(const String& hostname)
         prescientNetworking->prefetchDNS(hostname);
 }
 
-void preconnect(const KURL& url)
+void preconnect(const KURL& url, const CrossOriginAttributeValue crossOrigin)
 {
+    // TODO(yoav): Should send the crossOrigin data to the Chrome side.

[Mike West, 2015/05/11 12:53:35]

Why not define the new method in this patch and give it a default implementation
that forwards to the existing implementation? Then you'll have one less thing to
do in the patch where you remove the old implementation.

     if (WebPrescientNetworking* prescientNetworking = Platform::current()->prescientNetworking())
         prescientNetworking->preconnect(url);
 }