Pocket Door or Floor First
Flooring almost always goes in before trim work in new construction or remodeling because door jambs and casing should be fit to the tile for the best appearance. You don't want grout joints around woodwork if you can help it, and fitting tile under trim is a pain. 

You'll want to run tile a short distance into the pocket as well, as the edge will show under the door otherwise, lending to an unfinished appearance.

One related tip: Your pocket door probably comes with a rubber bumper installed on the rough frame behind the door. Once your split jambs are installed, seat the door fully and measure how far behind the jamb the door slab sits. Rip a strip of wood that thickness and attach it to the back edge of the slab where that bumper is. Now your door and jamb are flush when the door is open, which looks vastly more polished. The pull latch is also easier to grab than if the door sits back inside the slot too far.

Yet another unsolicited tip on pocket door installs: 1. Set the rough head rail level. 2. Set the full-width finish jamb plumb and straight. 3. Hang the door and plumb it using the hardware adjusters to mate nicely with the full jamb. 4. Open the door fully. 5. Set the side finish split jambs to parallel the edge of the door (not necessarily perfectly plumb). 5. Set the head split jambs.