Fix -Wnon-virtual-dtor compiler warnings.

core/include/fpdfdoc/fpdf_tagged.h

 // Copyright 2014 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 _FPDF_TAGGED_H_
 #define _FPDF_TAGGED_H_
 class CPDF_StructTree;
 class CPDF_StructElement;
@@ skipping 50 matching lines @@
 
             FX_DWORD                    m_PageObjNum;
 
             FX_DWORD                    m_RefObjNum;
         } m_Object;
     };
 };
 class CPDF_StructElement : public CFX_Object
 {
 public:
+    virtual ~CPDF_StructElement() { }
 
     virtual CPDF_StructTree*    GetTree() const = 0;
 
     virtual const CFX_ByteString&       GetType() const = 0;
 
     virtual CPDF_StructElement* GetParent() const = 0;
 
     virtual CPDF_Dictionary *   GetDict() const = 0;
 
     virtual int                                 CountKids() const = 0;
 
     virtual const CPDF_StructKid&       GetKid(int index) const = 0;
 
     virtual CFX_PtrArray*               GetObjectArray() = 0;
 
     virtual CPDF_Object*                GetAttr(FX_BSTR owner, FX_BSTR name, FX_BOOL bInheritable = FALSE, FX_FLOAT fLevel = 0.0F) = 0;
 
 
 
     virtual CFX_ByteString              GetName(FX_BSTR owner, FX_BSTR name, FX_BSTR default_value, FX_BOOL bInheritable = FALSE, int subindex = -1) = 0;
 
     virtual FX_ARGB                             GetColor(FX_BSTR owner, FX_BSTR name, FX_ARGB default_value, FX_BOOL bInheritable = FALSE, int subindex = -1) = 0;
 
     virtual FX_FLOAT                    GetNumber(FX_BSTR owner, FX_BSTR name, FX_FLOAT default_value, FX_BOOL bInheritable = FALSE, int subindex = -1) = 0;
 
     virtual int                                 GetInteger(FX_BSTR owner, FX_BSTR name, int default_value, FX_BOOL bInheritable = FALSE, int subindex = -1) = 0;
 
 };
 #endif