When the download folder does not exist, change the download folder to a user's "Downloads"

chrome/browser/download/download_prefs.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_PREFS_H_
 #define CHROME_BROWSER_DOWNLOAD_DOWNLOAD_PREFS_H_
 #pragma once
 
 #include <set>
 
 #include "base/file_path.h"
 #include "chrome/browser/prefs/pref_member.h"
 
+namespace download_test_util {
+class ScopedDefaultDownloadDirectory;
+}
+
 class PrefService;
 
 // Stores all download-related preferences.
 class DownloadPrefs {
  public:
   explicit DownloadPrefs(PrefService* prefs);
   ~DownloadPrefs();
 
   static void RegisterUserPrefs(PrefService* prefs);
 
@@ skipping 17 matching lines @@
 
   // Enables auto-open based on file extension. Returns true on success.
   // TODO(phajdan.jr): Add WARN_UNUSED_RESULT here.
   bool EnableAutoOpenBasedOnExtension(const FilePath& file_name);
 
   // Disables auto-open based on file extension.
   void DisableAutoOpenBasedOnExtension(const FilePath& file_name);
 
   void ResetAutoOpen();
 
+  FilePath GetDefaultDownloadDirectory();
+
  private:
+  friend class download_test_util::ScopedDefaultDownloadDirectory;
+
   void SaveAutoOpenState();
 
+  // This method can be used only through ScopedDefaultDownloadDirectory.
+  void OverrideDefaultDownloadDirectory(
+      const FilePath& override_default_download_dir);
+
+  // This method can be used only through ScopedDefaultDownloadDirectory.
+  void UnOverrideDefaultDownloadDirectory();
+
   PrefService* prefs_;
 
   BooleanPrefMember prompt_for_download_;
   FilePathPrefMember download_path_;
   IntegerPrefMember save_file_type_;
+  FilePath override_default_download_dir_;
 
   // Set of file extensions to open at download completion.
   struct AutoOpenCompareFunctor {
     bool operator()(const FilePath::StringType& a,
                     const FilePath::StringType& b) const;
   };
   typedef std::set<FilePath::StringType, AutoOpenCompareFunctor> AutoOpenSet;
   AutoOpenSet auto_open_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadPrefs);
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_PREFS_H_