Remove an unneeded variable in PDF's ScopedUnsupportedFeature.

pdf/pdfium/pdfium_engine.h

 // Copyright (c) 2012 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 PDF_PDFIUM_PDFIUM_ENGINE_H_
 #define PDF_PDFIUM_PDFIUM_ENGINE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 707 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(PDFiumEngine);
 };
 
 // Create a local variable of this when calling PDFium functions which can call
 // our global callback when an unsupported feature is reached.
 class ScopedUnsupportedFeature {
  public:
   explicit ScopedUnsupportedFeature(PDFiumEngine* engine);
   ~ScopedUnsupportedFeature();
+
  private:
-  PDFiumEngine* engine_;
-  PDFiumEngine* old_engine_;
+  PDFiumEngine* const old_engine_;
 };
 
 class PDFiumEngineExports : public PDFEngineExports {
  public:
   PDFiumEngineExports() {}
 
 // PDFEngineExports:
 #if defined(OS_WIN)
   bool RenderPDFPageToDC(const void* pdf_buffer,
                          int buffer_size,
@@ skipping 13 matching lines @@
   bool GetPDFPageSizeByIndex(const void* pdf_buffer,
                              int pdf_buffer_size,
                              int page_number,
                              double* width,
                              double* height) override;
 };
 
 }  // namespace chrome_pdf
 
 #endif  // PDF_PDFIUM_PDFIUM_ENGINE_H_