Roll WebGL 5b6cbd7..a2b3563

https://chromium.googlesource.com/external/khronosgroup/webgl.git/+log/5b6cbd7..a2b3563

Bug: 849576, 809237, 911918, angleproject:3012
Bug: 913301, 912842, 913033, 563816, 788439
Bug: angleproject:3033
Change-Id: I9b257afd69d26e75d1635633f556249583fdaa52
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
Reviewed-on: https://chromium-review.googlesource.com/c/1383329
Commit-Queue: James Darpinian <jdarpinian@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617754}
3 files changed