Use more unique_ptrs in CPDF_Image.

core/fpdfapi/page/cpdf_imageobject.h

 // Copyright 2016 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef CORE_FPDFAPI_PAGE_CPDF_IMAGEOBJECT_H_
 #define CORE_FPDFAPI_PAGE_CPDF_IMAGEOBJECT_H_
 
 #include <memory>
 
 #include "core/fpdfapi/page/cpdf_pageobject.h"
 #include "core/fxcrt/fx_coordinates.h"
 
 class CPDF_Image;
 
 class CPDF_ImageObject : public CPDF_PageObject {
  public:
   CPDF_ImageObject();
   ~CPDF_ImageObject() override;
 
   // CPDF_PageObject
-  CPDF_ImageObject* Clone() const override;
   Type GetType() const override;
   void Transform(const CFX_Matrix& matrix) override;
   bool IsImage() const override;
   CPDF_ImageObject* AsImage() override;
   const CPDF_ImageObject* AsImage() const override;
 
   void CalcBoundingBox();
   CPDF_Image* GetImage() const { return m_pImage; }
   void SetOwnedImage(std::unique_ptr<CPDF_Image> pImage);
   void SetUnownedImage(CPDF_Image* pImage);
 
   void set_matrix(const CFX_Matrix& matrix) { m_Matrix = matrix; }
   const CFX_Matrix& matrix() const { return m_Matrix; }
 
  private:
   void Release();
 
   CFX_Matrix m_Matrix;
   CPDF_Image* m_pImage;
   bool m_pImageOwned;
 };
 
 #endif  // CORE_FPDFAPI_PAGE_CPDF_IMAGEOBJECT_H_