uniquify

To avoid duplication, the `filename` is changed to include a counter before the filename extension.

overwrite

The existing file will be overwritten with the new file.

prompt

The user will be prompted with a file chooser dialog.

class FilenameConflictAction extends ChromeEnum {
 static const FilenameConflictAction UNIQUIFY = const FilenameConflictAction._('uniquify');
 static const FilenameConflictAction OVERWRITE = const FilenameConflictAction._('overwrite');
 static const FilenameConflictAction PROMPT = const FilenameConflictAction._('prompt');

 static const List<FilenameConflictAction> VALUES = const[UNIQUIFY, OVERWRITE, PROMPT];

 const FilenameConflictAction._(String str): super(str);
}