Fix UAF in chrome_pdf::Instance::GetURL()

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 <map>
 #include <string>
 #include <utility>
@@ skipping 26 matching lines @@
 class PDFiumEngine : public PDFEngine,
                      public DocumentLoader::Client,
                      public FPDF_FORMFILLINFO,
                      public IPDF_JSPLATFORM,
                      public IFSDK_PAUSE {
  public:
   explicit PDFiumEngine(PDFEngine::Client* client);
   virtual ~PDFiumEngine();
 
   // PDFEngine implementation.
+  virtual void ClientDestroyed();
   virtual bool New(const char* url);
   virtual bool New(const char* url,
                    const char* headers);
   virtual void PageOffsetUpdated(const pp::Point& page_offset);
   virtual void PluginSizeUpdated(const pp::Size& size);
   virtual void ScrolledToXPosition(int position);
   virtual void ScrolledToYPosition(int position);
   virtual void PrePaint();
   virtual void Paint(const pp::Rect& rect,
                      pp::ImageData* image_data,
@@ skipping 560 matching lines @@
 
   // See the definition of GetPDFPageSizeByIndex in pdf.cc for details.
   virtual bool GetPDFPageSizeByIndex(const void* pdf_buffer,
                                      int pdf_buffer_size, int page_number,
                                      double* width, double* height);
 };
 
 }  // namespace chrome_pdf
 
 #endif  // PDF_PDFIUM_PDFIUM_ENGINE_H_