For theater aficionados, the summer visits of Potomac Theatre Project to the Atlantic Theater are bracing—weighty pieces rather than fluffy fare. British writers, often well-represented, comprise one evening this year, but two American plays comprise the second. A revival of Dog Plays, a 1989 one-act with snapshot scenes that focus on the AIDS crisis, is by Robert Chesley, who wrote it after receiving “the diagnosis.” (He died in 1990.) It has been dusted off and paired with a new play, A Variant Strain, by writer-director Jim Petosa and Jonathan Adler, that is indebted to the older work.