Chrome: 71.0.3354.0 DEV

Steps to repro:
# Enable Chromevox with ctrl+alt+z
# Open file manager with alt+shift+m
# Navigate to the column headers with search+right arrow
# Notice that Chromevox does not indicate that these are clickable
# Click on a column header with search+space
# Notice that Chromevox does not announce anything about the new sort order
# Navigate away from and back to the column header with search+left and search+right arrow
# Notice that nothing about the header has changed

Expected: Labels would be links or buttons with help text to indicate that clicking on them would sort by that column. When clicked, Chromevox would announce the new sort order such as "Sorted by modified date, most recent first"
The label for the column heading would indicate that it is selected and the sort order is A-Z, or Z-A

Actual: Nothing is spoken