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

pdf/pdf_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_PDF_ENGINE_H_
 #define PDF_PDF_ENGINE_H_
 
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
@@ skipping 162 matching lines @@
     virtual void FormTextFieldFocusChange(bool in_focus) = 0;
 
     // Returns true if the plugin has been opened within print preview.
     virtual bool IsPrintPreview() = 0;
   };
 
   // Factory method to create an instance of the PDF Engine.
   static PDFEngine* Create(Client* client);
 
   virtual ~PDFEngine() {}
+
+  virtual void ClientDestroyed() {}
+
   // Most of these functions are similar to the Pepper functions of the same
   // name, so not repeating the description here unless it's different.
   virtual bool New(const char* url) = 0;
   virtual bool New(const char* url,
                    const char* headers) = 0;
   virtual void PageOffsetUpdated(const pp::Point& page_offset) = 0;
   virtual void PluginSizeUpdated(const pp::Size& size) = 0;
   virtual void ScrolledToXPosition(int position) = 0;
   virtual void ScrolledToYPosition(int position) = 0;
   // Paint is called a series of times. Before these n calls are made, PrePaint
@@ skipping 120 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) = 0;
 };
 
 }  // namespace chrome_pdf
 
 #endif  // PDF_PDF_ENGINE_H_