message: build: assert use_dawn
  This will help flush out future errors where targets depend on this
  target in configs where it won't build or isn't used.
diff: @@ -21,6 +21,13 @@ import("scripts/dawn_overrides_with_defaults.gni")
  import("//testing/test.gni")
  +if (build_with_chromium) {
  + # Chromium build targets may not depend on dawn unless use_dawn is set. This
  + # assertion helps avoid accidental dependencies creeping into chromium.
  + import("//ui/gl/features.gni")
  + assert(use_dawn)
  +}
  +
  ###############################################################################
  # dawn_platform
  ###############################################################################
  