Roll third_party/tint/ 67473c7a6..15ae496b0 (3 commits)

https://dawn.googlesource.com/tint/+log/67473c7a6c05..15ae496b042a

$ git log 67473c7a6..15ae496b0 --date=short --no-merges --format='%ad %ae %s'
2021-08-16 jrprice validation: disallow non-constructible assignments
2021-08-16 jrprice validation: disallow atomic type constructors
2021-08-16 bclayton writer/hlsl: UnwrapRef() on atomic types

Created with:
  roll-dep third_party/tint

No-Try: true
Change-Id: I981ee462f275478c34a227c46c8b962a88c6d552
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/62100
Auto-Submit: James Price <jrprice@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
diff --git a/DEPS b/DEPS
index 64eb743..b3621eb 100644
--- a/DEPS
+++ b/DEPS
@@ -96,7 +96,7 @@
 
   # WGSL support
   'third_party/tint': {
-    'url': '{dawn_git}/tint@67473c7a6c05ecfa3ff51108e1b82c91985601f8',
+    'url': '{dawn_git}/tint@15ae496b042a780cc1a40b74975dc177048d3522',
   },
 
   # GLFW for tests and samples