Roll ANGLE from a3f6dc2fadb4 to 900c7e87ce70 (2 revisions)

https://chromium.googlesource.com/angle/angle.git/+log/a3f6dc2fadb4..900c7e87ce70

2020-07-08 nguyenmh@google.com Serialize d/s buffers + use color buffers' impl format for readPixels
2020-07-08 jonahr@google.com Skip MultithreadingTest.MultiCreateContext on Ozone

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 syoussefi@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: chromium:1103009
Tbr: syoussefi@google.com
Change-Id: I09e8985100edb6814e1c1f25d4c7cda02fbfa88b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2288659Reviewed-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@{#786550}

DEPS

@@ -207,7 +207,7 @@ 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': 'a3f6dc2fadb487a6d53a94e9280d277537b275d6',
+  'angle_revision': '900c7e87ce707c081af72b51a5d08049a65c2fb8',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.