Add observer for BAAnnots from Javascript

fpdfsdk/cpdfsdk_widget.cpp

Index: fpdfsdk/cpdfsdk_widget.cpp
diff --git a/fpdfsdk/cpdfsdk_widget.cpp b/fpdfsdk/cpdfsdk_widget.cpp
index 73ba23d076a8feb0c9e198a0bb6f300136692c5c..c54c3eb9b8d3a3c836ba25759aa8e3d9de0be827 100644
--- a/fpdfsdk/cpdfsdk_widget.cpp
+++ b/fpdfsdk/cpdfsdk_widget.cpp
@@ -26,7 +26,6 @@
 #include "fpdfsdk/include/fsdk_mgr.h"
 #include "fpdfsdk/pdfwindow/PWL_Edit.h"
 #include "fpdfsdk/pdfwindow/PWL_Utils.h"
-#include "third_party/base/stl_util.h"
 
 #ifdef PDF_ENABLE_XFA
 #include "fpdfsdk/fpdfxfa/include/fpdfxfa_doc.h"
@@ -47,7 +46,7 @@ CPDFSDK_Widget::Observer::~Observer() {
     (*m_pWatchedPtr)->RemoveObserver(this);
 }
 
-void CPDFSDK_Widget::Observer::OnWidgetDestroyed() {
+void CPDFSDK_Widget::Observer::OnAnnotDestroyed() {
   ASSERT(m_pWatchedPtr);
   *m_pWatchedPtr = nullptr;
   m_pWatchedPtr = nullptr;
@@ -68,20 +67,7 @@ CPDFSDK_Widget::CPDFSDK_Widget(CPDF_Annot* pAnnot,
 {
 }
 
-CPDFSDK_Widget::~CPDFSDK_Widget() {
-  for (auto* pObserver : m_Observers)
-    pObserver->OnWidgetDestroyed();
-}
-
-void CPDFSDK_Widget::AddObserver(Observer* pObserver) {
-  ASSERT(!pdfium::ContainsKey(m_Observers, pObserver));
-  m_Observers.insert(pObserver);
-}
-
-void CPDFSDK_Widget::RemoveObserver(Observer* pObserver) {
-  ASSERT(pdfium::ContainsKey(m_Observers, pObserver));
-  m_Observers.erase(pObserver);
-}
+CPDFSDK_Widget::~CPDFSDK_Widget() {}
 
 #ifdef PDF_ENABLE_XFA
 CXFA_FFWidget* CPDFSDK_Widget::GetMixXFAWidget() const {