Get LinkProgram to work with int/uint sampler variables.

Get LinkProgram to work with int/uint sampler variables.

Otherwise, with shaders using these uniform types,
we encounter unknown uniform type and GPU process crash.

BUG=532708, 429053
TEST=conformance2/textures/canvas/*
R=piman@chromium.org

Committed: https://crrev.com/464af71ad16a3ba315058002976a84e09f6d68ad
Cr-Commit-Position: refs/heads/master@{#349320}

[Zhenyao Mo, 2015-09-16 23:46:50]

Verified.  With this, a bunch of WebGL 2 tests crash.  With this, they pass.

piman: PTAL

[Zhenyao Mo, 2015-09-16 23:46:55]

The CQ bit was checked by zmo@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-16 23:48:28]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1349793004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1349793004/1

[piman, 2015-09-16 23:50:36]

lgtm

[commit-bot: I haz the power, 2015-09-17 01:26:12]

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

[commit-bot: I haz the power, 2015-09-17 01:26:13]

Dry run: This issue passed the CQ dry run.

[Zhenyao Mo, 2015-09-17 02:01:44]

The CQ bit was checked by zmo@chromium.org

[commit-bot: I haz the power, 2015-09-17 02:02:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1349793004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1349793004/1

[commit-bot: I haz the power, 2015-09-17 02:07:30]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-17 02:08:30]

Patchset 1 (id:??) landed as
https://crrev.com/464af71ad16a3ba315058002976a84e09f6d68ad
Cr-Commit-Position: refs/heads/master@{#349320}