Disable use_dawn for the branch point

Bug: chromium:985142
Change-Id: Ifa9b692c47def3cbe1f3b030467a0bb122a2cfd9
TBR: cwallez@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1951895Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721788}

ui/gl/features.gni

@@ -14,5 +14,5 @@ declare_args() {
   # Should Dawn support be compiled to back the WebGPU implementation.
   # Also controls linking Dawn depedencies in such as SPIRV-Tools and
   # SPIRV-Cross
-  use_dawn = is_mac || is_win || is_chromeos
+  use_dawn = false
 }