Reland "Disable use_dawn for the branch point."

This reverts commit 1b433749.

Reason for revert: Next branch point

Original change's description:
> Revert "Disable use_dawn for the branch point."
> 
> This reverts commit b524af00.
> 
> Reason for revert: M78 has branched (r693954)
> 
> Original change's description:
> > Disable use_dawn for the branch point.
> > 
> > This flag controls the inclusion of Dawn and the availability of WebGPU
> > which we want to keep limited to Canary for now.
> > 
> > TBR=kbr@chromium.org
> > BUG=chromium:985142
> > 
> > Change-Id: I7677ec0571bcf394af4442829ad86e92a87b8a6b
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1784611
> > Reviewed-by: Corentin Wallez <cwallez@chromium.org>
> > Commit-Queue: Corentin Wallez <cwallez@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#693224}
> 
> TBR=kbr@chromium.org,cwallez@chromium.org
> 
> # Not skipping CQ checks because original CL landed > 1 day ago.
> 
> Bug: chromium:985142
> Change-Id: Ia5128d014026d46c0138d9a948b851856da5d310
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1789430
> Reviewed-by: Kai Ninomiya <kainino@chromium.org>
> Commit-Queue: Kai Ninomiya <kainino@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#694516}

TBR=kbr@chromium.org,cwallez@chromium.org,kainino@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:985142
Change-Id: If23eeb89a3130eafe1def72e293d60c0bd0222e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1867091Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707156}

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
+  use_dawn = false
 }