Add option to open PDFs in system viewer to OS X and Linux.

chrome/browser/download/download_shelf_context_menu.h

 // Copyright (c) 2011 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 CHROME_BROWSER_DOWNLOAD_DOWNLOAD_SHELF_CONTEXT_MENU_H_
 #define CHROME_BROWSER_DOWNLOAD_DOWNLOAD_SHELF_CONTEXT_MENU_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 57 matching lines @@
   void OnDownloadDestroyed(content::DownloadItem* download) override;
 
   ui::SimpleMenuModel* GetInProgressMenuModel();
   ui::SimpleMenuModel* GetFinishedMenuModel();
   ui::SimpleMenuModel* GetInterruptedMenuModel();
   ui::SimpleMenuModel* GetMaybeMaliciousMenuModel();
   ui::SimpleMenuModel* GetMaliciousMenuModel();
 
   int GetAlwaysOpenStringId() const;
 
-#if defined(OS_WIN)
+#if defined(OS_WIN) || defined(OS_LINUX) || \
+    (defined(OS_MACOSX) && !defined(OS_IOS))
   bool IsDownloadPdf() const;
   bool CanOpenPdfInReader() const;
 #endif
 
   // We show slightly different menus if the download is in progress vs. if the
   // download has finished.
   scoped_ptr<ui::SimpleMenuModel> in_progress_download_menu_model_;
   scoped_ptr<ui::SimpleMenuModel> finished_download_menu_model_;
   scoped_ptr<ui::SimpleMenuModel> interrupted_download_menu_model_;
   scoped_ptr<ui::SimpleMenuModel> maybe_malicious_download_menu_model_;
   scoped_ptr<ui::SimpleMenuModel> malicious_download_menu_model_;
 
   // Information source.
   content::DownloadItem* download_item_;
 
   // Used to open tabs.
   content::PageNavigator* navigator_;
 
 #if defined(OS_WIN)
   bool is_pdf_reader_up_to_date_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(DownloadShelfContextMenu);
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_SHELF_CONTEXT_MENU_H_