Get rid of code duplication in LinkRelAttribute

Source/core/html/LinkRelAttribute.h

 /*
  * 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 15 matching lines @@
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  */
 
 #ifndef LinkRelAttribute_h
 #define LinkRelAttribute_h
 
 #include "core/dom/IconURL.h"
-
-namespace WTF {
-class String;
-}
+#include "wtf/text/WTFString.h"
 
 namespace WebCore {
 
 class LinkRelAttribute {
 public:
-    LinkRelAttribute();
-    explicit LinkRelAttribute(const String&);
+    explicit LinkRelAttribute(const String& = "");
 
     bool isStyleSheet() const { return m_isStyleSheet; }
     IconType iconType() const { return m_iconType; }
     bool isAlternate() const { return m_isAlternate; }
     bool isDNSPrefetch() const { return m_isDNSPrefetch; }
     bool isLinkPrefetch() const { return m_isLinkPrefetch; }
     bool isLinkSubresource() const { return m_isLinkSubresource; }
     bool isLinkPrerender() const { return m_isLinkPrerender; }
     bool isLinkNext() const { return m_isLinkNext; }
     bool isImport() const { return m_isImport; }
 
 private:
     IconType m_iconType;
     bool m_isStyleSheet : 1;
     bool m_isAlternate : 1;
     bool m_isDNSPrefetch : 1;
     bool m_isLinkPrefetch : 1;
     bool m_isLinkSubresource : 1;
     bool m_isLinkPrerender : 1;
     bool m_isLinkNext : 1;
     bool m_isImport : 1;
 };
 
 }
 
 #endif