Revert of gpu: fix CopyTextureCHROMIUM for immutable texture.

Revert of gpu: fix CopyTextureCHROMIUM for immutable texture. (patchset #4 id:60001 of https://codereview.chromium.org/744713002/)

Reason for revert:
Broke video uploads to WebGL on official builds (taking the hardware accelerated video decode path). See Issue 436538.

Original issue's description:
> gpu: fix CopyTextureCHROMIUM for immutable texture.
>
> We cannot use glCopyTexImage2D on the texture which is allocated by glTexStorage2D [1]
> [1] https://www.opengl.org/registry/specs/ARB/texture_storage.txt
> The fast path uses glCopyTexSubImage2D instead of glCopyTexImage2D.
>
> In addition, optimize CopyTextureCHROMIUM for GL_TEXTURE_RECTANGLE_ARB,
> which is often used by the compositor, so make CopyTextureCHROMIUM use
> the fast path.
>
> Committed: https://crrev.com/df36f0aebe453bdbe842c85b331f6f07a24255a2
> Cr-Commit-Position: refs/heads/master@{#305268}

TBR=sievers@chromium.org,reveman@chromium.org,dongseong.hwang@intel.com
BUG=436538
Committed: https://crrev.com/e3558eac30baa00fe4bb4c1aa79f21185c98b485
Cr-Commit-Position: refs/heads/master@{#305937}

[Ken Russell (switch to Gerrit), 2014-11-27 00:48:14]

Created Revert of gpu: fix CopyTextureCHROMIUM for immutable texture.

[Ken Russell (switch to Gerrit), 2014-11-27 00:48:47]

Note: I'm sending this through the CQ to make sure nothing depended on the
original change.

[Ken Russell (switch to Gerrit), 2014-11-27 00:49:04]

The CQ bit was checked by kbr@chromium.org

[commit-bot: I haz the power, 2014-11-27 00:50:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/760173002/1

[commit-bot: I haz the power, 2014-11-27 01:50:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-11-27 01:51:07]

Patchset 1 (id:??) landed as
https://crrev.com/e3558eac30baa00fe4bb4c1aa79f21185c98b485
Cr-Commit-Position: refs/heads/master@{#305937}