Two new things here: 1) We append "Private" to the existing shortcut classification if it is likely to be a Private Browsing shortcut. (To help maintain the goal of avoiding I/O this is done by looking at the filename rather than inspecting the shortcut args.) 2) A totally new `is_taskbar_pinned_private` to report whether or not a Private Browsing shortcut is pinned to the Taskbar. Differential Revision: https://phabricator.services.mozilla.com/D140653