Roll SwiftShader from 7a1d99d0be42 to 974cfa9fbbdb (2 revisions)

https://swiftshader.googlesource.com/SwiftShader.git/+log/7a1d99d0be42..974cfa9fbbdb

2020-06-18 capn@google.com Optimize out-of-bounds checks with unsigned compare
2020-06-18 capn@google.com Replace instead of add pointer offsets when out of bounds

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/+doc/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: Ie6fa6928b3298e6bc329928add2afd80573b981d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2252518Reviewed-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@{#779935}

DEPS

@@ -198,7 +198,7 @@ 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': '7a1d99d0be42345b82c1d0c778a1ce69e6c20f34',
+  'swiftshader_revision': '974cfa9fbbdb72c25baef8d66e8e914e08631773',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.