message: Mark the audio_generator_factory target as testonly
  Cr-Commit-Position: refs/heads/master@{#28706}
diff: @@ -273,6 +273,7 @@ rtc_source_set("audio_generator_interface") {
  rtc_source_set("audio_generator_factory") {
  visibility = [ "*" ]
  + testonly = true
  sources = [
  "include/audio_generator_factory.cc",
  "include/audio_generator_factory.h",
  