Ensure vertical tabs are visible within deleted regions

Because we show tabs as red dotted lines, on a red background it
can be hard to see.  Use the heavier black dotted lines when the
tab is within either a whitespace error region or within a deleted
character region of a line.

Change-Id: I7e317127659d19ba80c9c22e4b8245e467c64fad
Signed-off-by: Shawn O. Pearce <sop@google.com>
1 file changed