Use dFdx in Vulkan to address distance field issues.

Use dFdx in Vulkan to address distance field issues.

On Nexus Player and occasionally Nexus 5x we get transparent boxes around
paths. This appears to be because the dFdy call is not as accurate as
dFdx, which is the opposite of Mali 400. As Mali 400 is not supported with
Vulkan, we can go back to using dFdx in this case.

BUG=skia:5523
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2163213004

Committed: https://skia.googlesource.com/skia/+/e499adf328bd7fc15a755325749f54c2b7e71f54

[jvanverth1, 2016-07-20 18:25:44]

Description was changed from

==========
Use dFdx in Vulkan to address distance field issues.

On Nexus Player and occasionally Nexus 5x we get transparent boxes around
paths. This appears to be because the dFdy call is not as accurate as
dFdx, which is the opposite of Mali 400. As Mali 400 is not supported with
Vulkan, we can go back to using dFdx in this case.

BUG=skia:5523
==========

to

==========
Use dFdx in Vulkan to address distance field issues.

On Nexus Player and occasionally Nexus 5x we get transparent boxes around
paths. This appears to be because the dFdy call is not as accurate as
dFdx, which is the opposite of Mali 400. As Mali 400 is not supported with
Vulkan, we can go back to using dFdx in this case.

BUG=skia:5523
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2163213004
==========

[jvanverth1, 2016-07-20 18:27:27]

jvanverth@google.com changed reviewers:
+ egdaniel@google.com

[egdaniel, 2016-07-20 18:36:40]

lgtm

[jvanverth1, 2016-07-20 18:47:17]

The CQ bit was checked by jvanverth@google.com

[commit-bot: I haz the power, 2016-07-20 18:47:30]

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, 2016-07-20 19:22:17]

Description was changed from

==========
Use dFdx in Vulkan to address distance field issues.

On Nexus Player and occasionally Nexus 5x we get transparent boxes around
paths. This appears to be because the dFdy call is not as accurate as
dFdx, which is the opposite of Mali 400. As Mali 400 is not supported with
Vulkan, we can go back to using dFdx in this case.

BUG=skia:5523
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2163213004
==========

to

==========
Use dFdx in Vulkan to address distance field issues.

On Nexus Player and occasionally Nexus 5x we get transparent boxes around
paths. This appears to be because the dFdy call is not as accurate as
dFdx, which is the opposite of Mali 400. As Mali 400 is not supported with
Vulkan, we can go back to using dFdx in this case.

BUG=skia:5523
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2163213004

Committed:
https://skia.googlesource.com/skia/+/e499adf328bd7fc15a755325749f54c2b7e71f54
==========

[commit-bot: I haz the power, 2016-07-20 19:22:17]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/e499adf328bd7fc15a755325749f54c2b7e71f54

[commit-bot: I haz the power, 2016-07-20 19:22:19]

CQ bit was unchecked.