GN: Tighten up test target visibility + refactorings

webrtc/modules/media_file/BUILD.gn

Index: webrtc/modules/media_file/BUILD.gn
diff --git a/webrtc/modules/media_file/BUILD.gn b/webrtc/modules/media_file/BUILD.gn
index 32825afb2beac863361bc85e388b6913a9573e7d..4f8fbbc4e28941288e384e0fb5220b2eee2774a0 100644
--- a/webrtc/modules/media_file/BUILD.gn
+++ b/webrtc/modules/media_file/BUILD.gn
@@ -43,6 +43,13 @@ rtc_static_library("media_file") {
 if (rtc_include_tests) {
   rtc_source_set("media_file_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/modules:modules_unittests" ]
+    }
     sources = [
       "media_file_unittest.cc",
     ]