Add observer for BAAnnots from Javascript

fpdfsdk/include/cpdfsdk_widget.h

Index: fpdfsdk/include/cpdfsdk_widget.h
diff --git a/fpdfsdk/include/cpdfsdk_widget.h b/fpdfsdk/include/cpdfsdk_widget.h
index 51116f9581421a9871f98a3be7b46d17259c2e88..88692d553e8d2a2b9af5394755e129b3fccb63e3 100644
--- a/fpdfsdk/include/cpdfsdk_widget.h
+++ b/fpdfsdk/include/cpdfsdk_widget.h
@@ -35,17 +35,6 @@ class CXFA_FFWidgetHandler;
 
 class CPDFSDK_Widget : public CPDFSDK_BAAnnot {
  public:
-  class Observer {
-   public:
-    explicit Observer(CPDFSDK_Widget** pWatchedPtr);
-    ~Observer();
-
-    void OnWidgetDestroyed();
-
-   private:
-    CPDFSDK_Widget** m_pWatchedPtr;
-  };
-
 #ifdef PDF_ENABLE_XFA
   CXFA_FFWidget* GetMixXFAWidget() const;
   CXFA_FFWidget* GetGroupMixXFAWidget();
@@ -75,9 +64,6 @@ class CPDFSDK_Widget : public CPDFSDK_BAAnnot {
                  CPDFSDK_InterForm* pInterForm);
   ~CPDFSDK_Widget() override;
 
-  void AddObserver(Observer* observer);
-  void RemoveObserver(Observer* observer);
-
   bool IsSignatureWidget() const override;
   CPDF_Action GetAAction(CPDF_AAction::AActionType eAAT) override;
   FX_BOOL IsAppearanceValid() override;
@@ -180,7 +166,6 @@ class CPDFSDK_Widget : public CPDFSDK_BAAnnot {
   FX_BOOL m_bAppModified;
   int32_t m_nAppAge;
   int32_t m_nValueAge;
-  std::set<Observer*> m_Observers;
 
 #ifdef PDF_ENABLE_XFA
   mutable CXFA_FFWidget* m_hMixXFAWidget;