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

chrome/browser/download/download_manager.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.
 //
 // The DownloadManager object manages the process of downloading, including
 // updates to the history system and providing the information for displaying
 // the downloads view in the Destinations tab. There is one DownloadManager per
 // active profile in Chrome.
 //
 // Download observers:
@@ skipping 68 matching lines @@
     // of downloads.
     virtual void ModelChanged() = 0;
 
     // Called when the DownloadManager is being destroyed to prevent Observers
     // from calling back to a stale pointer.
     virtual void ManagerGoingDown() {}
 
     // Called immediately after the DownloadManager puts up a select file
     // dialog.
     // |id| indicates which download opened the dialog.
-    virtual void SelectFileDialogDisplayed(int32 id) {}
+    // |suggested_path| indicates the path suggested in the dialog.
+    virtual void SelectFileDialogDisplayed(
+        int32 id, const FilePath& suggested_path) {}
 
    protected:
     virtual ~Observer() {}
   };
 
   // Return all temporary downloads that reside in the specified directory.
   void GetTemporaryDownloads(const FilePath& dir_path,
                              std::vector<DownloadItem*>* result);
 
   // Return all non-temporary downloads in the specified directory that are
@@ skipping 199 matching lines @@
   // Called on the UI thread if the FILE thread detects the removal of
   // the downloaded file. The UI thread updates the state of the file
   // and then notifies this update to the file's observer.
   void OnFileRemovalDetected(int64 db_handle);
 
   // Called on the download thread to check whether the suggested file path
   // exists.  We don't check if the file exists on the UI thread to avoid UI
   // stalls from interacting with the file system.
   void CheckIfSuggestedPathExists(int32 download_id,
                                   DownloadStateInfo state,
-                                  const FilePath& default_path);
+                                  const FilePath& download_save_dir,
+                                  const FilePath& default_download_dir);
 
   // Called on the UI thread once the DownloadManager has determined whether the
   // suggested file path exists.
   void OnPathExistenceAvailable(int32 download_id,
                                 DownloadStateInfo new_state);
 
   // Called back after a target path for the file to be downloaded to has been
   // determined, either automatically based on the suggested file name, or by
   // the user in a Save As dialog box.
   void ContinueDownloadWithPath(DownloadItem* download,
@@ skipping 104 matching lines @@
   // The "Save As" dialog box used to ask the user where a file should be
   // saved.
   scoped_refptr<SelectFileDialog> select_file_dialog_;
 
   scoped_ptr<OtherDownloadManagerObserver> other_download_manager_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadManager);
 };
 
 #endif  // CHROME_BROWSER_DOWNLOAD_DOWNLOAD_MANAGER_H_