Make code compile with clang_use_chrome_plugin (part I)

core/fpdfapi/fpdf_page/cpdf_contentmarkdata.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_FPDF_PAGE_CPDF_CONTENTMARKDATA_H_
 #define CORE_FPDFAPI_FPDF_PAGE_CPDF_CONTENTMARKDATA_H_
 
 #include <vector>
 
 #include "core/fpdfapi/fpdf_page/cpdf_contentmarkitem.h"
 #include "core/fxcrt/include/fx_system.h"
 
 class CPDF_Dictionary;
 
 class CPDF_ContentMarkData {
  public:
-  CPDF_ContentMarkData() {}
+  CPDF_ContentMarkData();
   CPDF_ContentMarkData(const CPDF_ContentMarkData& src);
+  ~CPDF_ContentMarkData();
 
   int CountItems() const;
-  CPDF_ContentMarkItem& GetItem(int index) { return m_Marks[index]; }
-  const CPDF_ContentMarkItem& GetItem(int index) const {
-    return m_Marks[index];
-  }
+  CPDF_ContentMarkItem& GetItem(int index);
+  const CPDF_ContentMarkItem& GetItem(int index) const;
 
   int GetMCID() const;
   void AddMark(const CFX_ByteString& name,
                CPDF_Dictionary* pDict,
                FX_BOOL bDictNeedClone);
   void DeleteLastMark();
 
  private:
   std::vector<CPDF_ContentMarkItem> m_Marks;
 };
 
 #endif  // CORE_FPDFAPI_FPDF_PAGE_CPDF_CONTENTMARKDATA_H_