Re-enable use_dawn after M81 branch point

Partial revert of https://crrev.com/c/2028649.

TBR: cwallez@chromium.org
Change-Id: Ib063064394c973f5feca87e7de5d343c1e77f6df
Bug: chromium:985142
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2033940Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#737566}

ui/gl/features.gni

@@ -13,9 +13,9 @@ declare_args() {
 
   # Should Dawn support be compiled to back the WebGPU implementation?
   # Also controls linking Dawn depedencies in such as SPIRV-Tools/SPIRV-Cross.
-  use_dawn = false
+  use_dawn = is_mac || is_win || is_chromeos
 
-  # Should Dawn test binaries (dawn_unittests, dawn_end2end_tests) be built?
+  # Should Dawn test binaries (unittests, end2end_tests, perf_tests) be built?
   # Independent of use_dawn, which controls whether Dawn is used in Chromium.
   build_dawn_tests = is_mac || is_win || is_linux
 }