image subsetting as part of the name instead of a separate source type

Image subsets as part of the name instead of a separate source type.

This will hold us closer to the principle that the test name (and only the test
name) should correspond to expected output.  By the same reasoning, mix in the
number of subsets: if that changes, the expected output also changes.

BUG=skia:3255
Committed: https://skia.googlesource.com/skia/+/9264a95608c08623f2955823703e5c77558cafa8

[mtklein, 2015-01-20 16:58:32]

mtklein@google.com changed reviewers:
+ mtklein@google.com, stephana@google.com

[mtklein, 2015-01-20 17:22:03]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-01-20 17:22:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/863723002/1

[commit-bot: I haz the power, 2015-01-20 17:22:37]

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 2015-01-20 23:22 UTC

[stephana, 2015-01-20 18:10:39]

On 2015/01/20 17:22:37, I haz the power (commit-bot) wrote:
> 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 2015-01-20 23:22 UTC

lgtm

[commit-bot: I haz the power, 2015-01-20 18:12:26]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/9264a95608c08623f2955823703e5c77558cafa8