Roll src/third_party/angle 50a47bd99229..7939e367fa53 (3 commits)

https://chromium.googlesource.com/angle/angle.git/+log/50a47bd99229..7939e367fa53

git log 50a47bd99229..7939e367fa53 --date=short --first-parent --format='%ad %ae %s'
2020-03-30 cwallez@chromium.org Revert "Enable blob cache when debugging"
2020-03-30 cnorthrop@google.com Vulkan: Expose extension for ETC1 usage with subimage updates
2020-03-30 courtneygo@google.com Enable blob cache when debugging

Created with:
  gclient setdep -r src/third_party/angle@7939e367fa53

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 cwallez@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/+/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
Bug: None
Tbr: cwallez@google.com
Change-Id: Iab1326e198ec7d61236f8a42298e18440bc3a0f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2127762Reviewed-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@{#754654}

DEPS

@@ -187,7 +187,7 @@ 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': '50a47bd992294216b0fe08db02bdd78746b56d8e',
+  'angle_revision': '7939e367fa53e4d730bd2af29791d876fac510a8',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.