CCPR: use 16-bit ints for the atlas offset attrib

Bug: skia:
Change-Id: I053e8416ced317b6ebc46cc8189840d60c7f91e8
Reviewed-on: https://skia-review.googlesource.com/62060
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
5 files changed