Revert of webgl: optimize webgl.texSubImage2D(video) path.

Revert of webgl: optimize webgl.texSubImage2D(video) path. (patchset #10 id:240001 of https://codereview.chromium.org/1315323006/ )

Reason for revert:
Reverting to address webgl_conformance_tests break in:

https://build.chromium.org/p/chromium.gpu/builders/Android%20Debug%20%28Nexus%209%29/builds/3534

Original issue's description:
> webgl: optimize webgl.texSubImage2D(video) path.
>
> Currently, texSubImage2D(video) requires glReadPixels to copy video texture to
> target texture. This CL makes infra structure to copy video texture to target
> texture directly. Blink will turn on the direct path.
>
> In addition, it will reduce WebGL video test flakiness significantly.
>
> TEST=video texture test on webgl_conformance
> ./content/test/gpu/run_gpu_test.py webgl_conformance --browser=release --story-filter=WebglConformance.conformance_textures_video_tex_image_and_sub_image_2d_with_video
> BUG=349871, 504773
>
> Committed: https://crrev.com/01542ac6d0fbec6aa78e33e6c7ec49a582072ea9
> Cr-Commit-Position: refs/heads/master@{#356390}

TBR=piman@chromium.org,dalecurtis@chromium.org,kbr@chromium.org,oetuaho@nvidia.com,dpranke@chromium.org,philipj@opera.com,dongseong.hwang@intel.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=349871, 504773
Committed: https://crrev.com/bfa196022345aa9bd694d200f107b6d809178715
Cr-Commit-Position: refs/heads/master@{#356415}

[dcaiafa, 2015-10-27 22:27:06]

Created Revert of webgl: optimize webgl.texSubImage2D(video) path.

[commit-bot: I haz the power, 2015-10-27 22:28:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1418513016/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1418513016/1

[commit-bot: I haz the power, 2015-10-27 22:30:06]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-27 22:30:47]

Patchset 1 (id:??) landed as
https://crrev.com/bfa196022345aa9bd694d200f107b6d809178715
Cr-Commit-Position: refs/heads/master@{#356415}