Roll WebGL aef0b3a..7c0541d

https://chromium.googlesource.com/external/khronosgroup/webgl.git/+log/aef0b3a..7c0541d

Bug: 804118, 818336, 828262, angleproject:2381
Tbr: zmo@chromium.org, kainino@chromium.org, jdarpinian@chromium.org
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_ng;luci.chromium.try:win_angle_rel_ng
Change-Id: I28b3d55e43f5633ffe4c8cd6e7e375dd2fba2b9b
Reviewed-on: https://chromium-review.googlesource.com/1010910
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550408}