Lacros: Fix xvfb condition in angle

For Lacros, xvfb is only used in Linux-Lacros, but not on-device
config, so this CL fixes the problem.

Bug: chromium:1195415
Test: built Chromium and Angle from source
Change-Id: Ia9adf706716c424b14a395189755932e445b7050
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2802854
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>

gni/angle.gni

@@ -408,7 +408,7 @@ if (angle_standalone || build_with_chromium) {
       }
 
       if ((is_linux && !is_chromeos) ||
-          (build_with_chromium && chromeos_is_browser_only)) {
+          (build_with_chromium && is_chromeos_lacros && !is_chromeos_device)) {
         use_xvfb = true
       }