Clean up singleton implementation

fpdfsdk/fpdfxfa/fpdfxfa_app.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/fpdfxfa/include/fpdfxfa_app.h"
 
 #include "fpdfsdk/fpdfxfa/include/fpdfxfa_util.h"
 #include "fpdfsdk/include/fsdk_define.h"
 #include "fpdfsdk/include/fsdk_mgr.h"
 #include "xfa/fxbarcode/include/BC_Library.h"
 #include "xfa/fxfa/include/xfa_ffapp.h"
 #include "xfa/fxfa/include/xfa_fontmgr.h"
 
-CPDFXFA_App* CPDFXFA_App::g_pApp = nullptr;
+namespace {
+
+CPDFXFA_App* g_pApp = nullptr;
+
+}  // namespace
 
 CPDFXFA_App* CPDFXFA_App::GetInstance() {
   if (!g_pApp) {
     g_pApp = new CPDFXFA_App();
   }
   return g_pApp;
 }
 
 void CPDFXFA_App::ReleaseInstance() {
   delete g_pApp;
@@ skipping 321 matching lines @@
   }
 }
 
 IFWL_AdapterTimerMgr* CPDFXFA_App::GetTimerMgr() {
   CXFA_FWLAdapterTimerMgr* pAdapter = nullptr;
   CPDFDoc_Environment* pEnv = m_pEnvList.GetAt(0);
   if (pEnv)
     pAdapter = new CXFA_FWLAdapterTimerMgr(pEnv);
   return pAdapter;
 }