Speed up centered hard stop shader

Reducing number of calls to GLSL mix() from two to one reduces frame render time by 21%

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2247113003

Committed: https://skia.googlesource.com/skia/+/af23ee538b5a007c2c9ca12ae6e54b2e0ed29876

[fmenozzi, 2016-08-16 14:01:14]

Description was changed from

==========
Speed up centered hard stop shader

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

to

==========
Speed up centered hard stop shader

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2247113003
==========

[fmenozzi, 2016-08-16 14:01:58]

fmenozzi@google.com changed reviewers:
+ tomhudson@google.com

[fmenozzi, 2016-08-16 14:01:59]

ptal

[tomhudson, 2016-08-16 14:05:42]

LGTM.

Nit: since you don't have a tracking bug, just a single sentence here in the CL
description about "changing from two mix() calls to one improves performance by
XX%" would be nice.

Also, why don't you have a tracking bug?

[fmenozzi, 2016-08-16 14:20:12]

Description was changed from

==========
Speed up centered hard stop shader

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2247113003
==========

to

==========
Reducing number of calls to GLSL mix() from two to one reduces frame render time
by 21%

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2247113003
==========

[fmenozzi, 2016-08-16 14:21:57]

The CQ bit was checked by fmenozzi@google.com

[commit-bot: I haz the power, 2016-08-16 14:22:04]

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, 2016-08-16 16:24:55]

Description was changed from

==========
Reducing number of calls to GLSL mix() from two to one reduces frame render time
by 21%

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2247113003
==========

to

==========
Reducing number of calls to GLSL mix() from two to one reduces frame render time
by 21%

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2247113003

Committed:
https://skia.googlesource.com/skia/+/af23ee538b5a007c2c9ca12ae6e54b2e0ed29876
==========

[commit-bot: I haz the power, 2016-08-16 16:24:56]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/af23ee538b5a007c2c9ca12ae6e54b2e0ed29876