Add observer for BAAnnots from Javascript

fpdfsdk/include/cpdfsdk_annot.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 FPDFSDK_INCLUDE_CPDFSDK_ANNOT_H_
 #define FPDFSDK_INCLUDE_CPDFSDK_ANNOT_H_
 
 #include "core/fpdfdoc/include/cpdf_aaction.h"
 #include "core/fpdfdoc/include/cpdf_annot.h"
 #include "core/fpdfdoc/include/cpdf_defaultappearance.h"
 #include "core/fxcrt/include/fx_basic.h"
 #include "fpdfsdk/cfx_systemhandler.h"
 #include "fpdfsdk/include/fsdk_common.h"
 #include "fpdfsdk/include/fsdk_define.h"
 
 class CFX_Matrix;
 class CFX_RenderDevice;
 class CPDF_Page;
 class CPDF_RenderOptions;
 class CPDFSDK_PageView;
 
 class CPDFSDK_Annot {
  public:
+  class Observer {
+   public:
+    explicit Observer(CPDFSDK_Annot** pWatchedPtr);
+    ~Observer();
+    void OnAnnotDestroyed();
+
+   private:
+    CPDFSDK_Annot** m_pWatchedPtr;
+  };
+
   explicit CPDFSDK_Annot(CPDFSDK_PageView* pPageView);
   virtual ~CPDFSDK_Annot();
 
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
 #ifdef PDF_ENABLE_XFA
   virtual FX_BOOL IsXFAField();
   virtual CXFA_FFWidget* GetXFAWidget() const;
 #endif  // PDF_ENABLE_XFA
 
   virtual FX_FLOAT GetMinWidth() const;
   virtual FX_FLOAT GetMinHeight() const;
   virtual int GetLayoutOrder() const;
   virtual CPDF_Annot* GetPDFAnnot() const;
   virtual CPDF_Annot::Subtype GetAnnotSubtype() const;
@@ skipping 11 matching lines @@
   CPDFXFA_Page* GetPDFXFAPage();
 #endif  // PDF_ENABLE_XFA
 
   void SetPage(CPDFSDK_PageView* pPageView);
   CPDFSDK_PageView* GetPageView() const { return m_pPageView; }
 
   FX_BOOL IsSelected();
   void SetSelected(FX_BOOL bSelected);
 
  protected:
+  std::set<Observer*> m_Observers;
   CPDFSDK_PageView* m_pPageView;
   FX_BOOL m_bSelected;
 };
 
 #endif  // FPDFSDK_INCLUDE_CPDFSDK_ANNOT_H_