The 1975 are currently the UK’s foremost exporters of bright and airy precision guitar music — think Phoenix but less aggressive, oblique, and uptight. They are closer to teen idols than rockers; take away their instruments and you might mistake them for a boy band. And like most other pop artists, their success is determined by how much sensory pleasure they can wring from their sugary confections. On those terms, Sunday afternoon they were totally sweet. Calling their best song “Chocolate” almost belabors the point.