Roll WebGL 6f0b34a..91350f8

https://chromium.googlesource.com/external/khronosgroup/webgl.git/+log/6f0b34a..91350f8

Bug: 763695, 949249, 953120, 958374
Bug: 961658, 979843, 980675
Bug: angleproject:1293, angleproject:3285, angleproject:3388, angleproject:3557
Cq-Include-Trybots: luci.chromium.try:win_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux-angle-rel;luci.chromium.try:win-angle-rel
Change-Id: I8e059ffc931e088176083e58351178b388feb56f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1684376
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#674292}
4 files changed