Use only headless Ozone on Cast audio-only platforms

BUG= internal b/32244773

Review-Url: https://codereview.chromium.org/2429963002
Cr-Commit-Position: refs/heads/master@{#441434}

chromecast/BUILD.gn

@@ -85,9 +85,13 @@ cast_test_group("cast_tests") {
       args = [
         "--no-sandbox",
         "--enable-local-file-accesses",
-        "--ozone-platform=cast",
         "--test-launcher-jobs=1",
       ]
+      if (is_cast_audio_only) {
+        args += [ "--ozone-platform=headless" ]
+      } else {
+        args += [ "--ozone-platform=cast" ]
+      }
       if (!is_cast_desktop_build) {
         args += [ "--use-gpu-in-tests" ]
 

ui/ozone/ozone.gni

@@ -33,7 +33,9 @@ declare_args() {
     ozone_platform = "headless"
     ozone_platform_headless = true
 
-    if (is_chromecast) {
+    if (is_cast_audio_only) {
+      # Just use headless for audio-only Cast platforms.
+    } else if (is_chromecast) {
       # Enable the Cast ozone platform on all A/V Cast builds.
       ozone_platform_cast = true