Add observer for BAAnnots from Javascript

fpdfsdk/cpdfsdk_annot.cpp

 // 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
 
 #include "fpdfsdk/include/cpdfsdk_annot.h"
 
 #include <algorithm>
 
 #include "fpdfsdk/include/fsdk_mgr.h"
+#include "third_party/base/stl_util.h"
 
 #ifdef PDF_ENABLE_XFA
 #include "fpdfsdk/fpdfxfa/include/fpdfxfa_doc.h"
 #endif  // PDF_ENABLE_XFA
 
 namespace {
 
 const float kMinWidth = 1.0f;
 const float kMinHeight = 1.0f;
 
 }  // namespace
 
+CPDFSDK_Annot::Observer::~Observer() {}
+
 CPDFSDK_Annot::CPDFSDK_Annot(CPDFSDK_PageView* pPageView)
     : m_pPageView(pPageView), m_bSelected(FALSE) {}
 
-CPDFSDK_Annot::~CPDFSDK_Annot() {}
+CPDFSDK_Annot::~CPDFSDK_Annot() {
+  for (auto* pObserver : m_Observers)
+    pObserver->OnAnnotDestroyed();
+}
+
+void CPDFSDK_Annot::AddObserver(Observer* pObserver) {
+  ASSERT(!pdfium::ContainsKey(m_Observers, pObserver));
+  m_Observers.insert(pObserver);
+}
+
+void CPDFSDK_Annot::RemoveObserver(Observer* pObserver) {
+  ASSERT(pdfium::ContainsKey(m_Observers, pObserver));
+  m_Observers.erase(pObserver);
+}
 
 #ifdef PDF_ENABLE_XFA
 
 FX_BOOL CPDFSDK_Annot::IsXFAField() {
   return FALSE;
 }
 
 CXFA_FFWidget* CPDFSDK_Annot::GetXFAWidget() const {
   return nullptr;
 }
@@ skipping 50 matching lines @@
 #ifdef PDF_ENABLE_XFA
   return GetPDFXFAPage();
 #else   // PDF_ENABLE_XFA
   return GetPDFPage();
 #endif  // PDF_ENABLE_XFA
 }
 
 CPDF_Page* CPDFSDK_Annot::GetPDFPage() {
   return m_pPageView ? m_pPageView->GetPDFPage() : nullptr;
 }