Roll src/third_party/swiftshader 5cf1e9a31c90..c66dad9552ef (6 commits)

https://swiftshader.googlesource.com/SwiftShader.git/+log/5cf1e9a31c90..c66dad9552ef

git log 5cf1e9a31c90..c66dad9552ef --date=short --first-parent --format='%ad %ae %s'
2020-04-01 bclayton@google.com Regres: Add invertCommon optimization.
2020-04-01 bclayton@google.com Regres: Move optimization logic to separate file
2020-04-01 bclayton@google.com Regres: Keep coverage span groups stable.
2020-04-01 bclayton@google.com Regres: Split coverage.go into multiple files
2020-04-01 bclayton@google.com Regres: Further optimizations for coverage
2020-04-01 bclayton@google.com Regres: Add cov.ReadJSON()

Created with:
  gclient setdep -r src/third_party/swiftshader@c66dad9552ef

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: I4bf210429838cc2de263f531f17da2c56b38fcca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2132508Reviewed-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@{#755428}

DEPS

@@ -191,7 +191,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling SwiftShader
   # and whatever else without interference from each other.
-  'swiftshader_revision': '5cf1e9a31c90ccd9ec40d0c5ef1357f6e0ec1cfd',
+  'swiftshader_revision': 'c66dad9552ef9cab3a4dfb66c22d756fc5c4b06c',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.