Roll src/third_party/SPIRV-Tools/src 8fa0f1a6567c..c18c9ff6bc30 (2 commits)

https://chromium.googlesource.com/external/github.com/KhronosGroup/SPIRV-Tools.git/+log/8fa0f1a6567c..c18c9ff6bc30

git log 8fa0f1a6567c..c18c9ff6bc30 --date=short --no-merges --format='%ad %ae %s'
2019-10-04 stevenperron@google.com Handle OpKill better (#2933)
2019-10-04 greg@lunarg.com Generate null pointer by converting uint64 zero to pointer. (#2935)

Created with:
  gclient setdep -r src/third_party/SPIRV-Tools/src@c18c9ff6bc30

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/spirv-tools-chromium-autoroll
Please CC radial-bots+chrome-roll@google.com,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_angle_vk32_deqp_rel_ng;luci.chromium.try:android_angle_vk32_rel_ng;luci.chromium.try:android_angle_vk64_deqp_rel_ng;luci.chromium.try:android_angle_vk64_rel_ng;luci.chromium.try:linux_angle_deqp_rel_ng;luci.chromium.try:linux-angle-rel;luci.chromium.try:win-angle-rel-32;luci.chromium.try:win-angle-rel-64;luci.chromium.try:win-angle-deqp-rel-32;luci.chromium.try:win-angle-deqp-rel-64
TBR=radial-bots+chrome-roll@google.com,geofflang@google.com

Bug: None
Change-Id: I31896afdb0faf401a9cb53270856885b14e67a9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1844073Reviewed-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@{#703243}

DEPS

@@ -286,7 +286,7 @@ vars = {
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling feed
   # and whatever else without interference from each other.
-  'spv_tools_revision': '8fa0f1a6567c55dcd50e1f42a3be5172789ef863',
+  'spv_tools_revision': 'c18c9ff6bc301f01b76319a818a975956abbf1d2',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling feed
   # and whatever else without interference from each other.