Tested on 57.0.2941.0 (platform 9052) and the performance is fine.

Tested on 58.0.3006.0 (platform 9265) and the performance is fine.

Tested on 58.0.3006.0 (platform 9266) and the performance is fine.

Tested on 58.0.3007.0 (platform 9267) and the performance regresses

Qiankun: FYI, https://codereview.chromium.org/2680703003 is the current likely suspect. Unfortunately, we'll have to revert and ask you to re-land if that's the one.

Yup that's the root cause. https://codereview.chromium.org/2695833003/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2404c8ae0098fa7cae48db92222240293a9d2689

commit 2404c8ae0098fa7cae48db92222240293a9d2689
Author: marcheu <marcheu@chromium.org>
Date: Tue Feb 14 02:48:52 2017

Revert of Select correct copy method for DoCopySubTexture (patchset #1 id:1 of https://codereview.chromium.org/2680703003/ )

Reason for revert:
The new DoCopySubTexture causes a performance regression on WebGL on Chrome OS.

BUG= chromium:691741 
TEST=on celes, webgl performance is back to normal

Original issue's description:
> Select correct copy method for DoCopySubTexture
>
> BUG= 687180 
> CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
>
> Review-Url: https://codereview.chromium.org/2680703003
> Cr-Commit-Position: refs/heads/master@{#448905}
> Committed: https://chromium.googlesource.com/chromium/src/+/a8450b810e89819add240a319586c899683dff9f

TBR=kbr@chromium.org,zmo@chromium.org,yunchao.he@intel.com,dongseong.hwang@intel.com,qiankun.miao@intel.com
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG= 687180 

Review-Url: https://codereview.chromium.org/2695833003
Cr-Commit-Position: refs/heads/master@{#450212}

[modify] https://crrev.com/2404c8ae0098fa7cae48db92222240293a9d2689/gpu/command_buffer/common/gles2_cmd_utils.cc
[modify] https://crrev.com/2404c8ae0098fa7cae48db92222240293a9d2689/gpu/command_buffer/common/gles2_cmd_utils.h
[modify] https://crrev.com/2404c8ae0098fa7cae48db92222240293a9d2689/gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.cc
[modify] https://crrev.com/2404c8ae0098fa7cae48db92222240293a9d2689/gpu/command_buffer/service/gles2_cmd_copy_texture_chromium.cc
[modify] https://crrev.com/2404c8ae0098fa7cae48db92222240293a9d2689/gpu/command_buffer/service/gles2_cmd_decoder.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/292b01d4c6d8f83a8973dc11ad76cdd63b1fb33c

commit 292b01d4c6d8f83a8973dc11ad76cdd63b1fb33c
Author: qiankun.miao <qiankun.miao@intel.com>
Date: Tue Feb 14 07:07:44 2017

Select correct copy method for DoCopySubTexture

BUG= 687180 ,  691741 
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2680703003
Cr-Commit-Position: refs/heads/master@{#450286}

[modify] https://crrev.com/292b01d4c6d8f83a8973dc11ad76cdd63b1fb33c/gpu/command_buffer/common/gles2_cmd_utils.cc
[modify] https://crrev.com/292b01d4c6d8f83a8973dc11ad76cdd63b1fb33c/gpu/command_buffer/common/gles2_cmd_utils.h
[modify] https://crrev.com/292b01d4c6d8f83a8973dc11ad76cdd63b1fb33c/gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.cc
[modify] https://crrev.com/292b01d4c6d8f83a8973dc11ad76cdd63b1fb33c/gpu/command_buffer/service/gles2_cmd_copy_texture_chromium.cc
[modify] https://crrev.com/292b01d4c6d8f83a8973dc11ad76cdd63b1fb33c/gpu/command_buffer/service/gles2_cmd_decoder.cc

How can I check if the performance was back with above CL?

Chrome hasn't upreved yet, otherwise it should be visible on the first links graph.

Chrome 3015 is good which contains your change in #13
https://chromium.googlesource.com/chromium/src/+log/58.0.3011.0..58.0.3015.0?pretty=fuller&n=10000

Verified on 9460.50.0/59.0.3071.71