Revert "Turn on WGSL support by default in Dawn"

This reverts commit e1d976ed9123ccbe8a9fa31ffb90c2b19fc53eb7.

Reason for revert: crbug.com/tint/123

Original change's description:
> Turn on WGSL support by default in Dawn
> 
> Tint is available in Chromium now, so we can turn this on. For situations were
> WGSL support is not needed it can still be turned off via args.gn.
> 
> Roll third_party/tint/ 16890b9ce..13904a612 (15 commits)
> 
> https://dawn.googlesource.com/tint/+log/16890b9ce8b7..5f43fedcd
> 
> $ git log 16890b9ce..5f43fedcd --date=short --no-merges --format='%ad %ae %s'
> 2020-07-16 rharrison Clean up how deps are defined in BUILD.gn
> 2020-07-16 dsinclair Remove refs.cfg.
> 2020-07-16 dsinclair Fixup group list name
> 2020-07-16 dsinclair [msl-writer] Emitting of program constants.
> 2020-07-16 dsinclair [msl-writer] Fixup matrix and array constructors.
> 2020-07-16 dsinclair Differentiate size and stride in array type name.
> 2020-07-16 dneto [spirv-reader] Support duplicate type definitions
> 2020-07-15 dsinclair [msl-writer] Add struct offset support.
> 2020-07-15 dsinclair [msl-writer] Add builtin support
> 2020-07-15 dsinclair Add helpers for referenced variables.
> 2020-07-15 dsinclair [msl-writer] Refactor some entry point variable code.
> 2020-07-15 dsinclair [msl-writer] Generate entry point functions.
> 2020-07-14 dsinclair [msl-writer] Handle emitting user function calls.
> 2020-07-14 dsinclair Inherit refererenced globals up the call stack.
> 2020-07-14 dsinclair [msl-writer] Generate input/output structs
> 
> Created with:
>   roll-dep third_party/tint
> 
> Change-Id: Ia437e8dc309b06a64ddd4d91ec3af1499af13553
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/24920
> Commit-Queue: Ryan Harrison <rharrison@chromium.org>
> Reviewed-by: dan sinclair <dsinclair@chromium.org>
> Reviewed-by: Ryan Harrison <rharrison@chromium.org>

TBR=cwallez@chromium.org,kainino@chromium.org,enga@chromium.org,dneto@google.com,rharrison@chromium.org,dsinclair@chromium.org

Change-Id: I21513d5b5d461eccd42aa650fa4b46e85daf642f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/25480
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
diff --git a/DEPS b/DEPS
index 7c18c31..fc97620 100644
--- a/DEPS
+++ b/DEPS
@@ -91,7 +91,7 @@
 
   # WGSL support
   'third_party/tint': {
-    'url': '{dawn_git}/tint@747e80a9b3695f6f694536a2bfde146f474873c3',
+    'url': '{dawn_git}/tint@18c85f52e482845079a26a22c9dfc633bf7a11a7',
     'condition': 'dawn_standalone',
   },
 
diff --git a/scripts/dawn_features.gni b/scripts/dawn_features.gni
index a0a38c2..1cee174 100644
--- a/scripts/dawn_features.gni
+++ b/scripts/dawn_features.gni
@@ -69,8 +69,9 @@
   # Whether Dawn should enable X11 support.
   dawn_use_x11 = is_linux && !is_chromeos
 
-  # Enable support WGSL for shaders.
-  dawn_enable_wgsl = true
+  # Enable support WGSL for shaders. Currently this is
+  # experimental, and requires dawn_tint_dir to be set.
+  dawn_enable_wgsl = false
 }
 
 # GN does not allow reading a variable defined in the same declare_args().