Cleanup GPU gamut transformation code

Two changes:

1. Remove special premul handling from gamut xform code

Alpha is a constant, so the gamut transformation results remain unchanged
(it distributes across the linear matrix multiply).

2. Use SkMatrix44 rather than array of floats

Preserves semantic intention, and makes upcoming code (where we transform
colors on the CPU by that matrix) simpler.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2329553002

Committed: https://skia.googlesource.com/skia/+/5192475bd8cb98e8e0c1192ab5ece7b8595701d6

[Brian Osman, 2016-09-09 18:52:28]

Description was changed from

==========
Remove special premul handling from gamut xform code

Alpha is a constant, so the gamut transformation results remain unchanged
(it distributes across the linear matrix multiply).

BUG=skia:
==========

to

==========
Remove special premul handling from gamut xform code

Alpha is a constant, so the gamut transformation results remain unchanged
(it distributes across the linear matrix multiply).

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2329553002
==========

[Brian Osman, 2016-09-09 18:53:03]

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

[commit-bot: I haz the power, 2016-09-09 18:53:04]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Brian Osman, 2016-09-09 18:53:29]

brianosman@google.com changed reviewers:
+ bsalomon@google.com, msarett@google.com, reed@google.com

[commit-bot: I haz the power, 2016-09-09 19:15:07]

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

[commit-bot: I haz the power, 2016-09-09 19:15:08]

Dry run: This issue passed the CQ dry run.

[Brian Osman, 2016-09-09 20:06:13]

Description was changed from

==========
Remove special premul handling from gamut xform code

Alpha is a constant, so the gamut transformation results remain unchanged
(it distributes across the linear matrix multiply).

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2329553002
==========

to

==========
Two changes:

1. Remove special premul handling from gamut xform code

Alpha is a constant, so the gamut transformation results remain unchanged
(it distributes across the linear matrix multiply).

2. Use SkMatrix44 rather than array of floats

Preserves semantic intention, and makes upcoming code (where we transform
colors on the CPU by that matrix) simpler.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2329553002
==========

[Brian Osman, 2016-09-09 20:06:30]

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

[commit-bot: I haz the power, 2016-09-09 20:06:31]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Brian Osman, 2016-09-09 20:07:16]

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

[Brian Osman, 2016-09-09 20:07:17]

Combined two useful refactorings together.

[commit-bot: I haz the power, 2016-09-09 20:25:40]

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

[commit-bot: I haz the power, 2016-09-09 20:25:41]

Dry run: This issue passed the CQ dry run.

[bsalomon, 2016-09-12 13:55:58]

lgtm

[Brian Osman, 2016-09-12 14:05:12]

The CQ bit was checked by brianosman@google.com

[commit-bot: I haz the power, 2016-09-12 14:05:16]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-12 15:50:21]

Description was changed from

==========
Two changes:

1. Remove special premul handling from gamut xform code

Alpha is a constant, so the gamut transformation results remain unchanged
(it distributes across the linear matrix multiply).

2. Use SkMatrix44 rather than array of floats

Preserves semantic intention, and makes upcoming code (where we transform
colors on the CPU by that matrix) simpler.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2329553002
==========

to

==========
Two changes:

1. Remove special premul handling from gamut xform code

Alpha is a constant, so the gamut transformation results remain unchanged
(it distributes across the linear matrix multiply).

2. Use SkMatrix44 rather than array of floats

Preserves semantic intention, and makes upcoming code (where we transform
colors on the CPU by that matrix) simpler.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2329553002

Committed:
https://skia.googlesource.com/skia/+/5192475bd8cb98e8e0c1192ab5ece7b8595701d6
==========

[commit-bot: I haz the power, 2016-09-12 15:50:22]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/5192475bd8cb98e8e0c1192ab5ece7b8595701d6