Add private PPAPI interfaces for PDFium accessibility.

ppapi/proxy/ppp_pdf_proxy.h

Index: ppapi/proxy/ppp_pdf_proxy.h
diff --git a/ppapi/proxy/ppp_pdf_proxy.h b/ppapi/proxy/ppp_pdf_proxy.h
index 5cc27900ac155893f28e1a5338fa2f765e045547..4f1f337980482465546b32702fe63f6bdbe186e3 100644
--- a/ppapi/proxy/ppp_pdf_proxy.h
+++ b/ppapi/proxy/ppp_pdf_proxy.h
@@ -5,6 +5,8 @@
 #ifndef PPAPI_PROXY_PPP_PDF_PROXY_H_
 #define PPAPI_PROXY_PPP_PDF_PROXY_H_
 
+#include <vector>
+
 #include "base/macros.h"
 #include "ppapi/c/private/ppp_pdf.h"
 #include "ppapi/proxy/interface_proxy.h"
@@ -29,6 +31,7 @@ class PPP_Pdf_Proxy : public InterfaceProxy {
   void OnPluginMsgPrintPresetOptions(PP_Instance instance,
                                      PP_PdfPrintPresetOptions_Dev* options,
                                      PP_Bool* result);
+  void OnPluginMsgEnableAccessibility(PP_Instance instance);
 
   // When this proxy is in the plugin side, this value caches the interface
   // pointer so we don't have to retrieve it from the dispatcher each time.