Validate page index in PDFiumEngine::ScrollToPage().

pdf/pdfium/pdfium_engine.h

Index: pdf/pdfium/pdfium_engine.h
diff --git a/pdf/pdfium/pdfium_engine.h b/pdf/pdfium/pdfium_engine.h
index 7826a5dcb57d4cc845fefcd232b4c12930bd5ece..89406c7dd3711fe807e51cd136efd61fcbd53f40 100644
--- a/pdf/pdfium/pdfium_engine.h
+++ b/pdf/pdfium/pdfium_engine.h
@@ -439,6 +439,8 @@ class PDFiumEngine : public PDFEngine,
   // Setting selection status of document.
   void SetSelecting(bool selecting);
 
+  bool PageIndexInBounds(int index) const;
+
   // FPDF_FORMFILLINFO callbacks.
   static void Form_Invalidate(FPDF_FORMFILLINFO* param,
                               FPDF_PAGE page,