be consistent about int for incReserve

Bug: 883666
Change-Id: I4070c958ef9ac5891ea75a8ef349e3d362c97f54
Reviewed-on: https://skia-review.googlesource.com/c/162620
Auto-Submit: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
(cherry picked from commit 6a388006f5e3b270d206fb4c7e24accadb1c790f)
Reviewed-on: https://skia-review.googlesource.com/c/170347
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Heather Miller <hcm@google.com>
5 files changed