[Line Layout API] Convert AbstractInlineTextBox to new line layout API

third_party/WebKit/Source/core/layout/api/LineLayoutTextCombine.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 LineLayoutTextCombine_h
 #define LineLayoutTextCombine_h
 
 #include "core/layout/LayoutTextCombine.h"
 #include "core/layout/api/LineLayoutText.h"
 
 namespace blink {
 
 class LineLayoutTextCombine : public LineLayoutText {
 public:
     explicit LineLayoutTextCombine(LayoutTextCombine* layoutTextCombine)
         : LineLayoutText(layoutTextCombine)
     {
     }
 
     explicit LineLayoutTextCombine(const LineLayoutItem& item)
         : LineLayoutText(item)
     {
         ASSERT(!item || item.isCombineText());
     }
 
+    LineLayoutTextCombine(std::nullptr_t) : LineLayoutText(nullptr) { }
+
     LineLayoutTextCombine() { }
 
     bool isCombined() const
     {
         return toTextCombine()->isCombined();
     }
 
 private:
     LayoutTextCombine* toTextCombine()
     {
         return toLayoutTextCombine(layoutObject());
     }
 
     const LayoutTextCombine* toTextCombine() const
     {
         return toLayoutTextCombine(layoutObject());
     }
 };
 
 } // namespace blink
 
 #endif // LineLayoutTextCombine_h