GN: Tighten up test target visibility + refactorings

webrtc/modules/bitrate_controller/BUILD.gn

Index: webrtc/modules/bitrate_controller/BUILD.gn
diff --git a/webrtc/modules/bitrate_controller/BUILD.gn b/webrtc/modules/bitrate_controller/BUILD.gn
index 58398f367fccac4d7d0db67bda7871f187995cfc..bb2bfb335f4382915b7e4e9854f15d503ee90602 100644
--- a/webrtc/modules/bitrate_controller/BUILD.gn
+++ b/webrtc/modules/bitrate_controller/BUILD.gn
@@ -46,6 +46,9 @@ rtc_static_library("bitrate_controller") {
 if (rtc_include_tests) {
   rtc_source_set("bitrate_controller_unittests") {
     testonly = true
+    if (!is_android && !is_ios) {  # Generated targets makes this check break.
+      visibility = [ "//webrtc/modules:modules_unittests" ]
+    }
     sources = [
       "bitrate_controller_unittest.cc",
       "send_side_bandwidth_estimation_unittest.cc",