add asserts on Sk4px::Map functions that our arrays are non-null.

add asserts on Sk4px::Map functions that our arrays are non-null.

There's a crasher (null dereference it looks like) in Clank with an impossible stack, but with blit mask on top (apparently sk_free() calls blit mask...).  Can't hurt to check that all these Sk4px-using methods are iterating over non-null arrays.

(This is that bug I mentioned that got me thinking about blit mask in the first place.)

BUG=520354
Committed: https://skia.googlesource.com/skia/+/15f4951e84a0aef2ed31b2e66129579feaa18850

[mtklein_C, 2015-08-13 14:20:35]

mtklein@chromium.org changed reviewers:
+ reed@google.com

[mtklein, 2015-08-13 14:31:52]

The CQ bit was checked by mtklein@google.com to run a CQ dry run

[commit-bot: I haz the power, 2015-08-13 14:31:55]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1295443002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1295443002/1

[reed1, 2015-08-13 14:35:38]

lgtm

[commit-bot: I haz the power, 2015-08-13 14:39:57]

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

[commit-bot: I haz the power, 2015-08-13 14:39:57]

Dry run: This issue passed the CQ dry run.

[mtklein, 2015-08-13 14:50:55]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-08-13 14:51:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1295443002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1295443002/1

[commit-bot: I haz the power, 2015-08-13 14:51:31]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/15f4951e84a0aef2ed31b2e66129579feaa18850