Roll src/third_party/swiftshader ab983012a2d4..514232c46d65 (3 commits)

https://swiftshader.googlesource.com/SwiftShader.git/+log/ab983012a2d4..514232c46d65

git log ab983012a2d4..514232c46d65 --date=short --first-parent --format='%ad %ae %s'
2020-04-16 bclayton@google.com VkSemaphore: Unlock/Lock the mutex outside the blocking_call.
2020-04-16 bclayton@google.com Regres: Include a better error message when git add fails.
2020-04-16 bclayton@google.com Regres: Avoid dereferencing a nil on process timeout.

Created with:
  gclient setdep -r src/third_party/swiftshader@514232c46d65

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/swiftshader-chromium-autoroll
Please CC swiftshader-team+autoroll@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_chromium_msan_rel_ng;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;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: swiftshader-team+autoroll@google.com
Change-Id: I420453664ba81032b803243ff03493f8c8994bdc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2152709
Reviewed-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@{#759706}