Do not unload pages while loading of the same pages is in progress.

pdf/pdfium/pdfium_page.h

 // Copyright (c) 2010 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_PAGE_H_
 #define PDF_PDFIUM_PDFIUM_PAGE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 16 matching lines @@
  public:
   PDFiumPage(PDFiumEngine* engine,
              int i,
              const pp::Rect& r,
              bool available);
   ~PDFiumPage();
   // Unloads the PDFium data for this page from memory.
   void Unload();
   // Gets the FPDF_PAGE for this page, loading and parsing it if necessary.
   FPDF_PAGE GetPage();
-  //Get the FPDF_PAGE for printing.
+  // Get the FPDF_PAGE for printing.
   FPDF_PAGE GetPrintPage();
-  //Close the printing page.
+  // Close the printing page.
   void ClosePrintPage();
 
   // Returns FPDF_TEXTPAGE for the page, loading and parsing it if necessary.
   FPDF_TEXTPAGE GetTextPage();
 
   // Returns a DictionaryValue version of the page.
   base::Value* GetAccessibleContentAsValue(int rotation);
 
   enum Area {
     NONSELECTABLE_AREA,
@@ skipping 55 matching lines @@
   Area GetLinkTarget(FPDF_LINK link, LinkTarget* target);
   // Returns target associated with a destination.
   Area GetDestinationTarget(FPDF_DEST destination, LinkTarget* target);
   // Returns the text in the supplied box as a Value Node
   base::Value* GetTextBoxAsValue(double page_height, double left, double top,
                                  double right, double bottom, int rotation);
   // Helper functions for JSON generation
   base::Value* CreateTextNode(std::string text);
   base::Value* CreateURLNode(std::string text, std::string url);
 
+  class ScopedLoadCounter {
+   public:
+    explicit ScopedLoadCounter(PDFiumPage* page);
+    ~ScopedLoadCounter();
+
+   private:
+    PDFiumPage* const page_;
+  };
+
   struct Link {
     Link();
     ~Link();
 
     std::string url;
     // Bounding rectangles of characters.
     std::vector<pp::Rect> rects;
   };
 
   PDFiumEngine* engine_;
   FPDF_PAGE page_;
   FPDF_TEXTPAGE text_page_;
   int index_;
+  int loading_count_;
   pp::Rect rect_;
   bool calculated_links_;
   std::vector<Link> links_;
   bool available_;
 };
 
 }  // namespace chrome_pdf
 
 #endif  // PDF_PDFIUM_PDFIUM_PAGE_H_