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

chrome/browser/download/download_prefs.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 CHROME_BROWSER_DOWNLOAD_DOWNLOAD_PREFS_H_
 #define CHROME_BROWSER_DOWNLOAD_DOWNLOAD_PREFS_H_
 
 #include <set>
 
 #include "base/files/file_path.h"
@@ skipping 62 matching lines @@
   // Disables auto-open based on file extension.
   void DisableAutoOpenBasedOnExtension(const base::FilePath& file_name);
 
 #if defined(OS_WIN)
   // Store the user preference to disk. If |should_open| is true, also disable
   // the built-in PDF plugin. If |should_open| is false, enable the PDF plugin.
   void SetShouldOpenPdfInAdobeReader(bool should_open);
 
   // Return whether the user prefers to open PDF downloads in Adobe Reader.
   bool ShouldOpenPdfInAdobeReader() const;
+#elif defined(OS_MACOSX) || defined(OS_LINUX)
+  // Store the user preference to disk. If |should_open| is true, also disable
+  // the built-in PDF plugin. If |should_open| is false, enable the PDF plugin.
+  void SetShouldOpenPdfInSystemReader(bool should_open);
+
+  // Return whether the user prefers to open PDF downloads in the platform's
+  // default reader.
+  bool ShouldOpenPdfInSystemReader() const;
 #endif
 
   void ResetAutoOpen();
 
  private:
   void SaveAutoOpenState();
 
   Profile* profile_;
 
   BooleanPrefMember prompt_for_download_;
   FilePathPrefMember download_path_;
   FilePathPrefMember save_file_path_;
   IntegerPrefMember save_file_type_;
 
   // Set of file extensions to open at download completion.
   struct AutoOpenCompareFunctor {
     bool operator()(const base::FilePath::StringType& a,
                     const base::FilePath::StringType& b) const;
   };
   typedef std::set<base::FilePath::StringType,
                    AutoOpenCompareFunctor> AutoOpenSet;
   AutoOpenSet auto_open_;
 
 #if defined(OS_WIN)
   bool should_open_pdf_in_adobe_reader_;
+#elif defined(OS_MACOSX) || defined(OS_LINUX)
+  bool should_open_pdf_in_system_reader_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(DownloadPrefs);
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_PREFS_H_