GrGLInterface: Add support for NV_framebuffer_mixed_samples

GrGLInterface: Add support for NV_framebuffer_mixed_samples

Import glCoverageModulation if NV_framebuffer_mixed samples
is available

BUG=skia:3177
Committed: https://skia.googlesource.com/skia/+/08b4d29a0a29badc15129c9bc7ee8352bc75278d

[vbuzinov, 2015-03-24 06:33:36]

vbuzinov@nvidia.com changed reviewers:
+ bsalomon@google.com

[vbuzinov, 2015-03-24 06:33:37]

Hi Brian, could you take a look?  This is patch 1 of 2 of
NV_framebuffer_mixed_samples implementation for skia.

[bsalomon, 2015-03-24 15:28:19]

On 2015/03/24 06:33:37, vbuzinov wrote:
> Hi Brian, could you take a look?  This is patch 1 of 2 of
> NV_framebuffer_mixed_samples implementation for skia.

lgtm

BTW I'm recovering from surgery last week. I'm just coming back part time
starting today. I'm also behind on stuff after being out for a week. Just a
heads up that I may be slow to respond for the next week.

[Chris Dalton, 2015-03-25 22:32:32]

cdalton@nvidia.com changed reviewers:
+ cdalton@nvidia.com

[Chris Dalton, 2015-03-25 22:32:33]

Should we add some validation code to the end of GrGLInterface::validate?

    if (fExtensions.has("GL_NV_framebuffer_mixed_samples")) {
        if (NULL == fFunctions.fCoverageModulation) {
            RETURN_FALSE_INTERFACE
        }
    }

[bsalomon, 2015-03-26 17:14:31]

On 2015/03/25 22:32:33, Chris Dalton wrote:
> Should we add some validation code to the end of GrGLInterface::validate?
> 
>     if (fExtensions.has("GL_NV_framebuffer_mixed_samples")) {
>         if (NULL == fFunctions.fCoverageModulation) {
>             RETURN_FALSE_INTERFACE
>         }
>     }

oh, yes, I missed that.

[vbuzinov, 2015-04-01 13:11:08]

Missed the validation comment, sorry, fixing that + rebasing

[bsalomon, 2015-04-01 13:21:57]

The CQ bit was checked by bsalomon@google.com

[bsalomon, 2015-04-01 13:21:58]

The patchset sent to the CQ was uploaded after l-g-t-m from bsalomon@google.com
Link to the patchset: https://codereview.chromium.org/993363002/#ps20001 (title:
"Rebase and missing validation")

[commit-bot: I haz the power, 2015-04-01 13:22:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/993363002/20001

[commit-bot: I haz the power, 2015-04-01 13:29:53]

Committed patchset #2 (id:20001) as
https://skia.googlesource.com/skia/+/08b4d29a0a29badc15129c9bc7ee8352bc75278d