Make Observers into a templated class

fpdfsdk/javascript/Annot.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_JAVASCRIPT_ANNOT_H_
 #define FPDFSDK_JAVASCRIPT_ANNOT_H_
 
 #include <memory>
 
 #include "fpdfsdk/include/cpdfsdk_baannot.h"
 #include "fpdfsdk/javascript/JS_Define.h"
 
-class Annot : public CJS_EmbedObj {
+class Annot : public CJS_EmbedObj, public CPDFSDK_Annot::Observer {
  public:
   explicit Annot(CJS_Object* pJSObject);
   ~Annot() override;
 
   FX_BOOL hidden(IJS_Context* cc, CJS_PropValue& vp, CFX_WideString& sError);
   FX_BOOL name(IJS_Context* cc, CJS_PropValue& vp, CFX_WideString& sError);
   FX_BOOL type(IJS_Context* cc, CJS_PropValue& vp, CFX_WideString& sError);
 
   void SetSDKAnnot(CPDFSDK_BAAnnot* annot);
 
  private:
   CPDFSDK_Annot* m_pAnnot = nullptr;
-  std::unique_ptr<CPDFSDK_Annot::Observer> m_pObserver;
 };
 
 class CJS_Annot : public CJS_Object {
  public:
   explicit CJS_Annot(v8::Local<v8::Object> pObject) : CJS_Object(pObject) {}
   ~CJS_Annot() override {}
 
   DECLARE_JS_CLASS();
   JS_STATIC_PROP(hidden, Annot);
   JS_STATIC_PROP(name, Annot);
   JS_STATIC_PROP(type, Annot);
 };
 
 #endif  // FPDFSDK_JAVASCRIPT_ANNOT_H_