Add private PPAPI interfaces for PDFium accessibility.

ppapi/c/private/ppp_pdf.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_C_PRIVATE_PPP_PDF_H_
 #define PPAPI_C_PRIVATE_PPP_PDF_H_
 
 #include <stdint.h>
 
 #include "ppapi/c/dev/pp_print_settings_dev.h"
@@ skipping 45 matching lines @@
   PP_Var (*GetLinkAtPosition)(PP_Instance instance,
                               PP_Point point);
 
   // Requests that the plugin apply the given transform to its view.
   void (*Transform)(PP_Instance instance, PP_PrivatePageTransformType type);
 
   // Return true if print preset options are updated from document.
   PP_Bool (*GetPrintPresetOptionsFromDocument)(
       PP_Instance instance,
       PP_PdfPrintPresetOptions_Dev* options);
+
+  void (*EnableAccessibility)(PP_Instance instance);
 };
 
 typedef PPP_Pdf_1_1 PPP_Pdf;
 
 #endif  // PPAPI_C_PRIVATE_PPP_PDF_H_