Roll SPIRV-Headers and SPIRV-Tools together to support new extensions.

Roll src/third_party/SPIRV-Tools/src/ 0cd3e599a..6e2dab2ff (3 commits)

$ git log 0cd3e599a..6e2dab2ff --date=short --no-merges --format='%ad %ae %s'
2018-09-19 chaoc Add support for Nvidia Turing extensions
2018-09-19 stevenperron Add unrolling to the legalization passes (#1903)
2018-09-17 jaebaek Specified clang-format version in README.md

Created with:
  roll-dep src/third_party/SPIRV-Tools/src

Roll src/third_party/spirv-headers/src/ dcf23bdab..d5b2e1255 (2 commits)

https://chromium.googlesource.com/external/github.com/KhronosGroup/SPIRV-Headers.git/+log/dcf23bdabacc..d5b2e1255f70

$ git log dcf23bdab..d5b2e1255 --date=short --no-merges --format='%ad %ae %s'
2018-09-19 cepheus Fix D -> d typo in previous commit.
2018-09-19 cepheus Add enumerants for six Nvidia extensions:

Created with:
  roll-dep src/third_party/spirv-headers/src

TBR=dneto@chromium.org

Change-Id: I024cb5917c5b0aaf61110a534ffa7d7b6664ab15
Reviewed-on: https://chromium-review.googlesource.com/1236373Reviewed-by: dsinclair <dsinclair@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592802}

DEPS

@@ -213,11 +213,11 @@ 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': '0cd3e599ae3b3179c26b0e0756f0b488a9d82b7e',
+  'spv_tools_revision': '6e2dab2ffd46a5cf62e2edd3908b4351eaf193d1',
   # 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_headers_revision': 'dcf23bdabacc3c54b83b1f9367e7a8adb27f8d87',
+  'spv_headers_revision': 'd5b2e1255f706ce1f88812217e9a554f299848af',
 }
 
 # Only these hosts are allowed for dependencies in this DEPS file.