Top extra bars at discontinues edges is preferable if spacing exceeds 300mm at top, as partial fixity condition may arise.
You may provide extra bars if it is framed structure, and if the slab is monolithic with the edge beam due to fixity. Otherwise there may be some cracks will develop before the moment is thrown to the span from support. If it is simply supported say on masonry wall or so, then no extra bars are required. At least one third of span steel should be provided at the end at top.
Also for partial fixity at the corners square mesh is needed. Even if it a one way slab it is necessary to provide some top bars at the ends of longitudinal span supports (parallel to the longitudinal direction distribution bars.
Also See: Reinforcement Detailing in Concrete Structures