Currently, PopupMenuStyle has TextDirection field, but not field for text alignment. Webkit align popup left when using natural writing direction. It would be useful to add text alignment in PopupMenuStyle so that each client could draw text using the desired alignment and text direction, such as align popup right but display menu item in natural writing direction. Related Bug 19785, Bug 38749, Bug 29612, and chromium issue 6139 (http://crbug.com/6139)
refer to http://trac.webkit.org/changeset/76983 for detail.