Revert "Replaced all calls to fragmentPosition() with sk_FragCoord"

This reverts commit de4d301881e7fd084f1f0b359ec6f9b2bf8bd4c5.

Reason for revert: several Chrome rendering bugs on Mac

BUG=skia:

Change-Id: I492082b0b7e7c902ede4b598c5809f604d210ce1
Reviewed-on: https://skia-review.googlesource.com/7887
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
32 files changed