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

base/path_service.h

Index: base/path_service.h
diff --git a/base/path_service.h b/base/path_service.h
index 284fbf7e9536950c4952ff95603530809ca690b7..2f295856da3c8af8d83b734726529c92b8b36ae5 100644
--- a/base/path_service.h
+++ b/base/path_service.h
@@ -20,14 +20,18 @@ class FilePath;
 class BASE_API PathService {
  public:
   // Retrieves a path to a special directory or file and places it into the
-  // string pointed to by 'path'. If you ask for a directory it is guaranteed
+  // string pointed to by |path|. If you ask for a directory it is guaranteed
   // to NOT have a path separator at the end. For example, "c:\windows\temp"
   // Directories are also guaranteed to exist when this function succeeds.
   //
   // Returns true if the directory or file was successfully retrieved. On
-  // failure, 'path' will not be changed.
+  // failure, |path| will not be changed.
   static bool Get(int key, FilePath* path);
 
+  // Sets a path to a special directory or file. This overwrites the current
+  // path of the special directory or file. |path| may be a non-existent path.
+  static void Set(int key, const FilePath& path);
+
   // Overrides the path to a special directory or file.  This cannot be used to
   // change the value of DIR_CURRENT, but that should be obvious.  Also, if the
   // path specifies a directory that does not exist, the directory will be