Roll src/third_party/angle 4d2040a6f973..78da538aed52 (4 commits)

https://chromium.googlesource.com/angle/angle.git/+log/4d2040a6f973..78da538aed52

git log 4d2040a6f973..78da538aed52 --date=short --first-parent --format='%ad %ae %s'
2020-02-27 rnk@chromium.org Revert "Vulkan: Disable global merge for volk"
2020-02-27 jmadill@chromium.org Capture/Replay: Capture DrawBuffersEXT.
2020-02-27 jmadill@chromium.org Fix out-of-bounds read in test.
2020-02-27 jonahr@google.com eglGetConfigAttrib validation missing extension check

Created with:
  gclient setdep -r src/third_party/angle@78da538aed52

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 geofflang@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: chromium:1015454
Tbr: geofflang@google.com
Change-Id: Ia8d67711c2e59d0511bee0a76c06f00a663fd1f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2079347Reviewed-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@{#745262}

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': '4d2040a6f9737e27e65e17343abb337ac292777d',
+  'angle_revision': '78da538aed5268be4bab9f230f101bf57b93d462',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.