Roll ANGLE from b6ea6edc3f4e to 973bd4ba0f57 (2 revisions)

https://chromium.googlesource.com/angle/angle.git/+log/b6ea6edc3f4e..973bd4ba0f57

2021-01-05 syoussefi@chromium.org Complete I/O block GLSL tests
2021-01-05 syoussefi@chromium.org Vulkan: Directly capture non-gl_Postion builtins

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/angle-chromium-autoroll
Please CC ianelliott@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/master/autoroll/README.md

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win-asan;luci.chromium.try:win_optional_gpu_tests_rel;luci.chromium.try:linux-swangle-try-x64;luci.chromium.try:win-swangle-try-x86
Bug: None
Tbr: ianelliott@google.com
Change-Id: I0eb3e3310acfee7c00a703944d0a47180cbbc997
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2611165Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#840277}

DEPS

@@ -211,7 +211,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling ANGLE
   # and whatever else without interference from each other.
-  'angle_revision': 'b6ea6edc3f4e6487e30a5716cfccbf02c8f4a174',
+  'angle_revision': '973bd4ba0f5775c66b6811bf81f6483e629365c7',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.