Warner Bros. and producer Joel Silver are working with Mattel to turn “He-Man and the Masters of the Universe” into a live-action film. Justin Marks is set to write the script. Silver will produce. Deal, which is contingent on Mattel formally approving an outline for the project, is another example of Hollywood overhauling a 1980s-era pop-culture touchstone in the hopes of seeding a tentpole film. The sale comes just a few weeks before the July premiere of DreamWorks’ Michael Bay-directed “Transformers,” which began as an ’80s animated series and toy line.