Fix incorrect override of GetLayoutOrder().

fpdfsdk/include/fsdk_baseform.h

 // 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
 
 #ifndef _FSDK_BASEFORM_H_
 #define _FSDK_BASEFORM_H_
 
 #if _FX_OS_ == _FX_ANDROID_
@@ skipping 42 matching lines @@
 public:
         CPDFSDK_Widget(CPDF_Annot* pAnnot, CPDFSDK_PageView* pPageView, CPDFSDK_InterForm* pInterForm);
         virtual ~CPDFSDK_Widget();
 
         virtual CFX_ByteString                  GetSubType() const;
         
         virtual CPDF_Action                             GetAAction(CPDF_AAction::AActionType eAAT);
 
         int                                                             GetFieldType() const;
         //define layout order to 2.
-        virtual int                                             GetLayoutOrder() {return 2;}
+        virtual int                                             GetLayoutOrder() const {return 2;}
         /*
         FIELDFLAG_READONLY
         FIELDFLAG_REQUIRED
         FIELDFLAG_NOEXPORT
         */
         
         int                                                             GetFieldFlags() const;
         int                                                             GetRotate() const;
 
         FX_BOOL                                                 GetFillColor(FX_COLORREF& color) const;
@@ skipping 209 matching lines @@
         CPDFSDK_PageView*                                       m_pPageView;
         CFX_ByteString                                          m_sType;
         CFX_ByteString                                          m_sSubType;
         int                                                                     m_nTabs;
         
         CPDFSDK_Annots                                          m_Annots;
 };
 
 #endif //#define _FSDK_BASEFORM_H_