This replaces all GYP-based iOS bots with one new GN-based one.
Ordinarily I'd do this more incrementally but we have only one iPad.
This new bot will start very broken, but should be the quickest
to cycle builds once I get it working.
Change-Id: I41865e3ad431dea3cf023d0b33ccc88e175cf227
Reviewed-on: https://skia-review.googlesource.com/7941
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
