GN: Tighten up test target visibility + refactorings

webrtc/tools/network_tester/BUILD.gn

Index: webrtc/tools/network_tester/BUILD.gn
diff --git a/webrtc/tools/network_tester/BUILD.gn b/webrtc/tools/network_tester/BUILD.gn
index 1e290f60cfa8e8058a8b65d64e551b9fad406eef..5fd3ac9b7fec06f3101b45674994ec72af79a329 100644
--- a/webrtc/tools/network_tester/BUILD.gn
+++ b/webrtc/tools/network_tester/BUILD.gn
@@ -68,11 +68,18 @@ if (rtc_enable_protobuf) {
   }
 
   rtc_source_set("network_tester_unittests") {
+    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/tools:tools_unittests" ]
+    }
     sources = [
       "network_tester_unittest.cc",
     ]
 
-    testonly = true
     deps = [
       ":network_tester",
       "//testing/gtest",