Add SkMiniData.

Add SkMiniData.

This is a bit like a limited SkData, geared to store really tiny byte strings.

This is not hooked up anywhere beyond the new unit test.  I did experimentally
plumb it into SkRecord for drawPosTextH: just over 40% of drawPosTextH calls in
our repo can fit into ShortData.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/6a5c7085bcebe263ac43486f1825407580662924

[mtklein, 2014-09-17 17:56:33]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-09-17 17:56:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/573323002/40001

[commit-bot: I haz the power, 2014-09-17 17:57:00]

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 a valid reviewer till 2014-09-17 23:56 UTC

[mtklein, 2014-09-17 18:00:52]

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

[reed1, 2014-09-17 18:19:20]

lgtm

[mtklein, 2014-09-17 18:35:23]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-09-17 18:35:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/573323002/60001

[commit-bot: I haz the power, 2014-09-17 19:22:03]

Committed patchset #4 (id:60001) as 6a5c7085bcebe263ac43486f1825407580662924