Rolling 2 dependencies

Roll third_party/SPIRV-Tools/ 18b3b9456..f8d7df760 (2 commits)

https://chromium.googlesource.com/external/github.com/KhronosGroup/SPIRV-Tools/+log/18b3b94567a9..f8d7df760c81

$ git log 18b3b9456..f8d7df760 --date=short --no-merges --format='%ad %ae %s'
2020-01-14 jaebaek Fix OpLine bug of merge-blocks pass (#3130)
2020-01-13 afdx spirv-fuzz: add dead blocks (#3135)

Roll third_party/shaderc/ dc2172c08..df0e683b5 (4 commits)

https://chromium.googlesource.com/external/github.com/google/shaderc/+log/dc2172c083f6..df0e683b5835

$ git log dc2172c08..df0e683b5 --date=short --no-merges --format='%ad %ae %s'
2020-01-15 rharrison Fix incorrect casing on flags in docs (#957)
2020-01-14 rharrison Convert get_shader_resources to return ptr instead of ref (#955)
2020-01-14 rharrison Convert spvc messages internal struct to be a vector (#952)
2020-01-13 rharrison Rolling 5 dependencies (#953)

Created with:
  roll-dep third_party/SPIRV-Tools third_party/glslang third_party/shaderc third_party/spirv-cross third_party/spirv-headers

Change-Id: Ib97af2147dd6c17f9e71ff1c3cf8200e4b353fdc
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/15160
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
diff --git a/DEPS b/DEPS
index b7676bd..7875e8f 100644
--- a/DEPS
+++ b/DEPS
@@ -57,7 +57,7 @@
 
   # SPIRV compiler dependencies: SPIRV-Tools, SPIRV-headers, glslang and shaderc
   'third_party/SPIRV-Tools': {
-    'url': '{chromium_git}/external/github.com/KhronosGroup/SPIRV-Tools@18b3b94567a9251a6f8491a6d07c4422abadd22c',
+    'url': '{chromium_git}/external/github.com/KhronosGroup/SPIRV-Tools@f8d7df760c81604ddc4ae3dac7f19333336f64c3',
     'condition': 'dawn_standalone',
   },
   'third_party/spirv-headers': {
@@ -69,7 +69,7 @@
     'condition': 'dawn_standalone',
   },
   'third_party/shaderc': {
-    'url': '{chromium_git}/external/github.com/google/shaderc@dc2172c083f6ac0ba8c1c609d64a2edd0fa8b81b',
+    'url': '{chromium_git}/external/github.com/google/shaderc@df0e683b583580fcdf5670d05de76a82f39aedcb',
     'condition': 'dawn_standalone',
   },