Roll WebGL 73fd432..40d75ac

https://chromium.googlesource.com/external/khronosgroup/webgl.git/+log/73fd432..40d75ac

BUG=
TBR=zmo@chromium.org
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/2837473003
Cr-Commit-Position: refs/heads/master@{#466399}
3 files changed