Add unit and layout test to <link rel=preconnect>

Source/core/loader/NetworkHintsInterface.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NetworkHintsInterface_h
+#define NetworkHintsInterface_h
+
+#include "platform/network/NetworkHints.h"
+
+namespace blink {
+
+class NetworkHintsInterface {
+public:
+    virtual void dnsPrefetchHost(const String&) const = 0;
+    virtual void preconnectHost(const KURL&, const CrossOriginAttributeValue) const = 0;
+};
+
+class NetworkHintsInterfaceImpl : public NetworkHintsInterface {
+    void dnsPrefetchHost(const String& host) const override
+    {
+        prefetchDNS(host);
+    }
+
+    void preconnectHost(const KURL& host, const CrossOriginAttributeValue crossOrigin) const override
+    {
+        preconnect(host, crossOrigin);
+    }
+};
+
+} // namespace blink
+
+#endif