Roll src/third_party/swiftshader 793b6c3d0b6b..69ffc317eb39 (3 commits)

https://swiftshader.googlesource.com/SwiftShader.git/+log/793b6c3d0b6b..69ffc317eb39

git log 793b6c3d0b6b..69ffc317eb39 --date=short --no-merges --format='%ad %ae %s'
2019-08-30 capn@google.com Initialize the blend state using memset
2019-08-29 sugoi@google.com Add VK_IMAGE_USAGE_SAMPLED_BIT to SurfaceKHR
2019-08-29 sugoi@google.com Support for independentBlend feature

Created with:
  gclient setdep -r src/third_party/swiftshader@69ffc317eb39

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
TBR=swiftshader-team+autoroll@google.com

Bug: chromium:b/140286664,chromium:b/140193782
Change-Id: Idabb325ceb200af6d4a8564a2690a675f4a5f980
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1778582Reviewed-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@{#692092}

DEPS

@@ -178,7 +178,7 @@ 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': '793b6c3d0b6b466eb58502aded624176683fed9d',
+  'swiftshader_revision': '69ffc317eb3960f18e9d70cb8c3ade94ed4ac399',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFium
   # and whatever else without interference from each other.