Factor out common BorderImageLength code in CSSToStyleMap

Source/core/rendering/style/BorderImageLength.h

 /*
  * Copyright (c) 2013, Opera Software ASA. 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 23 matching lines @@
 #include "platform/Length.h"
 
 namespace WebCore {
 
 // Represents an individual computed border image width or outset.
 //
 // http://www.w3.org/TR/css3-background/#border-image-width
 // http://www.w3.org/TR/css3-background/#border-image-outset
 class BorderImageLength {
 public:
-    BorderImageLength()
-        : m_length(Auto)
-        , m_number(0)
-        , m_type(LengthType)
-    {
-    }
-
     BorderImageLength(double number)
         : m_length(Undefined)
         , m_number(number)
         , m_type(NumberType)
     {
     }
 
     BorderImageLength(const Length& length)
         : m_length(length)
         , m_number(0)
@@ skipping 26 matching lines @@
     double m_number;
     enum {
         LengthType,
         NumberType
     } m_type;
 };
 
 } // namespace WebCore
 
 #endif // BorderImageLength_h