cast SK_ARRAY_COUNT to make it sign agnostic

cast SK_ARRAY_COUNT to make it sign agnostic

By adding a cast to SK_ARRAY_COUNT, the compiler treats the
compile-time value as if it were a const int, and like regular
numbers, permits it to be compared to signed and unsigned
numbers freely.

R=reed@google.com

Committed: https://skia.googlesource.com/skia/+/bca86202a48b2afa527b6e40d8b360ce3bc7c2e7

[caryclark, 2015-08-18 18:05:51]

The CQ bit was checked by caryclark@google.com

[commit-bot: I haz the power, 2015-08-18 18:06:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1299943002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1299943002/1

[commit-bot: I haz the power, 2015-08-18 18:06:04]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2015-08-19 00:06 UTC

[commit-bot: I haz the power, 2015-08-18 18:06:55]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-18 18:06:56]

Try jobs failed on following builders:
  skia_presubmit-Trybot on client.skia.fyi (JOB_FAILED,
http://build.chromium.org/p/client.skia.fyi/builders/skia_presubmit-Trybot/bu...)

[reed1, 2015-08-19 15:26:48]

The CQ bit was checked by reed@google.com

[reed1, 2015-08-19 15:26:48]

lgtm

[commit-bot: I haz the power, 2015-08-19 15:26:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1299943002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1299943002/1

[commit-bot: I haz the power, 2015-08-19 15:28:19]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/bca86202a48b2afa527b6e40d8b360ce3bc7c2e7

[caryclark, 2015-08-19 17:12:44]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1285263007/ by caryclark@google.com.

The reason for reverting is: fails on chrome build on windows.