converted arithmetic FP to new FP structure

Bug: skia:
Change-Id: I5492b378fa0f2ab7b453b2b1b18e4aef898370d2
Reviewed-on: https://skia-review.googlesource.com/148910
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
15 files changed