gpu: Don't clear texture level in DoCopyTexSubImage2D() if not needed.

gpu: Don't clear texture level in DoCopyTexSubImage2D() if not needed.

This optimization is similar to one of TexSubImage2D().

TEST=Service/GLES2DecoderTest.CopyTexSubImage2DClearsUnclearedBackBufferSizedTexture

Committed: https://crrev.com/351519fd09084647cd154169c0d1f99181e029bb
Cr-Commit-Position: refs/heads/master@{#312371}

[dshwang, 2015-01-19 18:25:37]

dongseong.hwang@intel.com changed reviewers:
+ piman@chromium.org, sievers@chromium.org

[dshwang, 2015-01-19 18:26:06]

could you review this small optimization for glCopyTexSubImage2D?

[piman, 2015-01-20 19:17:09]

LGTM, but could you add a unit test?

[dshwang, 2015-01-20 20:53:10]

On 2015/01/20 19:17:09, piman (Very slow to review) wrote:
> LGTM, but could you add a unit test?

Thank you for reviewing. I add
gpu_unittests.Service/GLES2DecoderTest.CopyTexSubImage2DClearsUnclearedBackBufferSizedTexture
Could you review again?

[piman, 2015-01-20 22:07:33]

LGTM, thanks!

[dshwang, 2015-01-20 22:16:59]

The CQ bit was checked by dongseong.hwang@intel.com

[commit-bot: I haz the power, 2015-01-20 22:24:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/824173003/20001

[commit-bot: I haz the power, 2015-01-20 23:24:53]

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

[commit-bot: I haz the power, 2015-01-20 23:24:54]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[dshwang, 2015-01-21 12:59:52]

The CQ bit was checked by dongseong.hwang@intel.com

[commit-bot: I haz the power, 2015-01-21 13:02:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/824173003/20001

[commit-bot: I haz the power, 2015-01-21 14:34:30]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-01-21 14:36:35]

Patchset 2 (id:??) landed as
https://crrev.com/351519fd09084647cd154169c0d1f99181e029bb
Cr-Commit-Position: refs/heads/master@{#312371}