pass size_t to ptr_and_ix()

dx and dy are already size_t, so no need to demote them to int,
and demoting to int gets dicey in terms of wrap-around.

Change-Id: I98eb31ef7aa35fa2c2aa5be27cdc0b4dc7dfd008
Reviewed-on: https://skia-review.googlesource.com/99500
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
3 files changed