"THE THIN RED LINE." Glass Tiger. Manhattan. Glass Tiger is the newest cog in Canadian pop's hit-making machinery, assisted here by such big wheels as Bryan Adams and his songwriting partner Jim Vallance. Adams contributes backup vocals to "Don't Forget Me (When I'm Gone)," a song that, for all its catchiness, is pretty thin: It gets its point across with the title, but goes on for another four minutes. That's characteristic of Glass Tiger's expansive, well-crafted fluff. Most of the material putters along a wholly commercial path, unencumbered by minor concerns like substance or originality.