GN: Tighten up test target visibility + refactorings

webrtc/audio/BUILD.gn

Index: webrtc/audio/BUILD.gn
diff --git a/webrtc/audio/BUILD.gn b/webrtc/audio/BUILD.gn
index 0de4229c7be8ce9416dfb8088cf23a9e4914d338..b3d4e1d89ef4052cd5e47bc1d4094b1345a8bf44 100644
--- a/webrtc/audio/BUILD.gn
+++ b/webrtc/audio/BUILD.gn
@@ -54,6 +54,13 @@ if (rtc_include_tests) {
   rtc_source_set("audio_tests") {
     testonly = true
 
+    # Skip restricting visibility on mobile platforms since the tests on those
+    # gets additional generated targets which would require many lines here to
+    # cover (which would be confusing to read and hard to maintain).
+    if (!is_android && !is_ios) {
+      visibility = [ "//webrtc:video_engine_tests" ]
+    }
+
     # TODO(kjellander): Remove (bugs.webrtc.org/6828)
     # This needs remote_bitrate_estimator to be moved to webrtc/api first.
     check_includes = false