Watch destruction of widgets around OnAAction() method

fpdfsdk/formfiller/cffl_checkbox.cpp

 // 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
 
 #include "fpdfsdk/formfiller/cffl_checkbox.h"
 
 #include "fpdfsdk/formfiller/cffl_formfiller.h"
 #include "fpdfsdk/include/cpdfsdk_environment.h"
@@ skipping 29 matching lines @@
                               uint32_t nChar,
                               uint32_t nFlags) {
   switch (nChar) {
     case FWL_VKEY_Return:
     case FWL_VKEY_Space: {
       CPDFSDK_PageView* pPageView = pAnnot->GetPageView();
       ASSERT(pPageView);
 
       FX_BOOL bReset = FALSE;
       FX_BOOL bExit = FALSE;
-      m_pEnv->GetInteractiveFormFiller()->OnButtonUp(m_pWidget, pPageView,
+      CPDFSDK_Annot::ObservedPtr pObserved(m_pWidget);
+      m_pEnv->GetInteractiveFormFiller()->OnButtonUp(&pObserved, pPageView,
                                                      bReset, bExit, nFlags);
-      if (bReset)
+      if (!pObserved) {
+        m_pWidget = nullptr;
         return TRUE;
-      if (bExit)
+      }
+      if (bReset || bExit)
         return TRUE;
 
       CFFL_FormFiller::OnChar(pAnnot, nChar, nFlags);
-
       if (CPWL_CheckBox* pWnd = (CPWL_CheckBox*)GetPDFWindow(pPageView, TRUE))
         pWnd->SetCheck(!pWnd->IsChecked());
 
       CommitData(pPageView, nFlags);
       return TRUE;
     }
     default:
       return CFFL_FormFiller::OnChar(pAnnot, nChar, nFlags);
   }
 }
@@ skipping 35 matching lines @@
           }
         }
       }
     }
 
     m_pWidget->SetCheck(bNewChecked, false);
     m_pWidget->UpdateField();
     SetChangeMark();
   }
 }