Use enum class for subtypes of CPDF_Annot.

fpdfsdk/include/cpdfsdk_baannot.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 FPDFSDK_INCLUDE_CPDFSDK_BAANNOT_H_
 #define FPDFSDK_INCLUDE_CPDFSDK_BAANNOT_H_
 
 #include "core/fpdfdoc/include/cpdf_aaction.h"
@@ skipping 10 matching lines @@
 class CPDF_Dictionary;
 class CPDF_RenderOptions;
 class CPDFSDK_PageView;
 
 class CPDFSDK_BAAnnot : public CPDFSDK_Annot {
  public:
   CPDFSDK_BAAnnot(CPDF_Annot* pAnnot, CPDFSDK_PageView* pPageView);
   ~CPDFSDK_BAAnnot() override;
 
   // CPDFSDK_Annot
-  CFX_ByteString GetAnnotSubtype() const override;
+  CPDF_Annot::Subtype GetAnnotSubtype() const override;
   void SetRect(const CFX_FloatRect& rect) override;
   CFX_FloatRect GetRect() const override;
   CPDF_Annot* GetPDFAnnot() const override;
   void Annot_OnDraw(CFX_RenderDevice* pDevice,
                     CFX_Matrix* pUser2Device,
                     CPDF_RenderOptions* pOptions) override;
 
   CPDF_Dictionary* GetAnnotDict() const;
   CPDF_Annot* GetPDFPopupAnnot() const;
 
@@ skipping 55 matching lines @@
                        const CFX_ByteString& sContents,
                        const CFX_ByteString& sAPState = "");
 
   void SetOpenState(bool bState);
 
  protected:
   CPDF_Annot* m_pAnnot;
 };
 
 #endif  // FPDFSDK_INCLUDE_CPDFSDK_BAANNOT_H_