Restore groups as a single entry in 'recently closed"
Currently, when a user right-clicks on a group header and chooses "Close Group", each tab in the group gets is own entry in TabRestore and there is no way to restore the group as a whole.
This CL creates a new TabRestore entry type for tab groups. Then, when a user right-clicks on a group header and chooses "Close Group", the group entry is stored as a single item. The group will then restore as a unit, similar to windows.
Individual tabs that are part of a group can still be closed independently, resulting in separate tab entries. When those tabs are restored, the group will still be recreated in the tabstrip. If the group itself is also closed, the individual tabs and group will merge together in the tabstrip at the time of restore.