Convert Field to use CPDFSDK_FormFillEnvironment

fpdfsdk/cpdfsdk_formfillenvironment.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_CPDFSDK_FORMFILLENVIRONMENT_H_
 #define FPDFSDK_CPDFSDK_FORMFILLENVIRONMENT_H_
 
 #include <memory>
 
 #include "core/fpdfapi/page/cpdf_page.h"
 #include "core/fpdfapi/parser/cpdf_document.h"
 #include "core/fpdfdoc/cpdf_occontext.h"
 #include "core/fxcrt/cfx_observable.h"
 #include "fpdfsdk/cfx_systemhandler.h"
 #include "fpdfsdk/fsdk_define.h"
 #include "public/fpdf_formfill.h"
 #include "public/fpdf_fwlevent.h"
 
 class CFFL_InteractiveFormFiller;
 class CFX_SystemHandler;
 class CPDFSDK_ActionHandler;
 class CPDFSDK_AnnotHandlerMgr;
 class CPDFSDK_Document;
 class IJS_Runtime;
 
-class CPDFSDK_FormFillEnvironment final {
+class CPDFSDK_FormFillEnvironment
+    : public CFX_Observable<CPDFSDK_FormFillEnvironment> {
  public:
   CPDFSDK_FormFillEnvironment(UnderlyingDocumentType* pDoc,
                               FPDF_FORMFILLINFO* pFFinfo);
   ~CPDFSDK_FormFillEnvironment();
 
   void Invalidate(FPDF_PAGE page,
                   double left,
                   double top,
                   double right,
                   double bottom);
@@ skipping 127 matching lines @@
   std::unique_ptr<CPDFSDK_ActionHandler> m_pActionHandler;
   std::unique_ptr<IJS_Runtime> m_pJSRuntime;
   FPDF_FORMFILLINFO* const m_pInfo;
   std::unique_ptr<CPDFSDK_Document> m_pSDKDoc;
   UnderlyingDocumentType* const m_pUnderlyingDoc;
   std::unique_ptr<CFFL_InteractiveFormFiller> m_pFormFiller;
   std::unique_ptr<CFX_SystemHandler> m_pSysHandler;
 };
 
 #endif  // FPDFSDK_CPDFSDK_FORMFILLENVIRONMENT_H_