Revert "Disable use_dawn for the branch point"

This reverts commit 9e845692.

Reason for revert: M80 branched @{#722274}

Original change's description:
> 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/+/1951895
> Reviewed-by: Kai Ninomiya <kainino@chromium.org>
> Commit-Queue: Kai Ninomiya <kainino@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#721788}

TBR=kainino@chromium.org

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

Bug: chromium:985142, chromium:1031607
Change-Id: I4690e9cb042047c4d06db8412c0bb8729469857d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1955087Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#722694}

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 = false
+  use_dawn = is_mac || is_win || is_chromeos
 }