Warner Bros. has strong-armed Guillermo del Toro to convert “Pacific Rim” to 3D.The alien invasion pic, which bows July 12, has all the ingredients for a 3D tentpole — giant robots vs. aliens in a planet-wide battle to save humanity. But at Comic-Con in July, del Toro said he was resistant to converting the film to 3D because of the scale and size of the pic’s creatures. The director has never released a 3D pic. In the end, the prospect of the 3D upcharge — especially overseas — was likely too much for Warners to resist. Some naysayers criticized Universal for not releasing similar alien invasion pic “Battleship” in 3D. The big-budget misfire certainly would have paid for its 3D conversion internationally at least. Warner, meanwhile, has been more bullish with the format. (Consider “Wrath of the Titans.”) “Pacific Rim,” starring Idris Elba, Charlie Hunnam and Charlie Day, is produced by Legendary Pictures’ Thomas Tull and Jon Jashni. Travis Beacham wrote the screenplay. Warner, which also will offer “Pacific Rim” in 2D, expects to finish the pic’s conversion in time for a mid-July release date.