[pdf] Defer page unloading in JS callback.

pdf/pdfium/pdfium_engine.cc

 // 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.
 
 #include "pdf/pdfium/pdfium_engine.h"
 
 #include <math.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 2269 matching lines @@
       return -1;
     dest = FPDFBookmark_GetDest(doc_, bookmark);
   }
   return dest ? FPDFDest_GetPageIndex(doc_, dest) : -1;
 }
 
 int PDFiumEngine::GetMostVisiblePage() {
   if (in_flight_visible_page_)
     return *in_flight_visible_page_;
 
+  // We can call GetMostVisiblePage through a callback from PDFium. We have
+  // to defer the page deletion otherwise we could potentially delete the page
+  // that originated the calling JS request and destroy the objects that are
+  // currently being used.
+  defer_page_unload_ = true;
   CalculateVisiblePages();
+  defer_page_unload_ = false;
   return most_visible_page_;
 }
 
 pp::Rect PDFiumEngine::GetPageRect(int index) {
   pp::Rect rc(pages_[index]->rect());
   rc.Inset(-kPageShadowLeft, -kPageShadowTop,
            -kPageShadowRight, -kPageShadowBottom);
   return rc;
 }
 
@@ skipping 1674 matching lines @@
   FPDF_DOCUMENT doc =
       FPDF_LoadMemDocument(pdf_buffer, pdf_buffer_size, nullptr);
   if (!doc)
     return false;
   bool success = FPDF_GetPageSizeByIndex(doc, page_number, width, height) != 0;
   FPDF_CloseDocument(doc);
   return success;
 }
 
 }  // namespace chrome_pdf