I created a WebGL conformance test to reproduce this bug: https://github.com/KhronosGroup/WebGL/pull/2369.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9589135cc575bcaeb2b730df193ca9cbc408cec4

commit 9589135cc575bcaeb2b730df193ca9cbc408cec4
Author: qiankun.miao <qiankun.miao@intel.com>
Date: Wed Apr 19 17:53:53 2017

Roll WebGL fd73a60..73fd432

https://chromium.googlesource.com/external/khronosgroup/webgl.git/+log/fd73a60..73fd432

BUG= 708730 ,  712584 ,  712117 ,  713127 ,  angleproject:1966 

TEST=bots

CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.win:win_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2820113008
Cr-Commit-Position: refs/heads/master@{#465664}

[modify] https://crrev.com/9589135cc575bcaeb2b730df193ca9cbc408cec4/DEPS
[modify] https://crrev.com/9589135cc575bcaeb2b730df193ca9cbc408cec4/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
[modify] https://crrev.com/9589135cc575bcaeb2b730df193ca9cbc408cec4/content/test/gpu/gpu_tests/webgl_conformance_expectations.py
[modify] https://crrev.com/9589135cc575bcaeb2b730df193ca9cbc408cec4/content/test/gpu/gpu_tests/webgl_conformance_revision.txt

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9d28c22de85528d1f87bfbf3f88dc531027b24bd

commit 9d28c22de85528d1f87bfbf3f88dc531027b24bd
Author: qiankun.miao <qiankun.miao@intel.com>
Date: Thu Apr 20 06:22:07 2017

Force cube map texture complete on Linux AMD

CopyTex{Sub}Image2D reports INVALID_OPERATION error if the destination
texture is an integer incomplete cube map texture on Linux AMD. Similarly,
TexSubImage2D reports OUT_OF_MEMORY error if the destination texture is a
srgb incomplete cube map texture on Linux AMD. This is a bug in AMD Linux
driver. This CL workarounds this bug by forcing the texture to be cube map
complete.

BUG=710392,  712117 
TEST=webgl2 conformance test
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;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/2821913002
Cr-Commit-Position: refs/heads/master@{#465915}

[modify] https://crrev.com/9d28c22de85528d1f87bfbf3f88dc531027b24bd/gpu/command_buffer/service/gles2_cmd_decoder.cc
[modify] https://crrev.com/9d28c22de85528d1f87bfbf3f88dc531027b24bd/gpu/command_buffer/service/texture_manager.cc
[modify] https://crrev.com/9d28c22de85528d1f87bfbf3f88dc531027b24bd/gpu/command_buffer/service/texture_manager.h
[modify] https://crrev.com/9d28c22de85528d1f87bfbf3f88dc531027b24bd/gpu/config/gpu_driver_bug_list.json
[modify] https://crrev.com/9d28c22de85528d1f87bfbf3f88dc531027b24bd/gpu/config/gpu_driver_bug_workaround_type.h

The following conformance tests are still failing due to this bug:
WebglConformance_conformance2_textures_canvas_tex_2d_rg8ui_rg_integer_unsigned_byte
WebglConformance_conformance2_textures_canvas_tex_2d_rgb8ui_rgb_integer_unsigned_byte
WebglConformance_conformance2_textures_canvas_tex_2d_rgba8ui_rgba_integer_unsigned_byte
WebglConformance_conformance2_textures_webgl_canvas_tex_2d_rg8ui_rg_integer_unsigned_byte
WebglConformance_conformance2_textures_webgl_canvas_tex_2d_rgb8ui_rgb_integer_unsigned_byte
WebglConformance_conformance2_textures_webgl_canvas_tex_2d_rgba8ui_rgba_integer_unsigned_byte

Part of the bug is workaround. If all faces of the cube texture is undefined, we force the cube texture to be cube complete by filling zeros. But, if some faces of the cube texture is already defined, we cannot do that since it might modify user defined data.

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

Sorry for the inconvenience if the bug really should have been left as Available.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

I think this is a small enough case to call it WontFix.