GN: Tighten up test target visibility + refactorings

webrtc/modules/video_processing/BUILD.gn

Index: webrtc/modules/video_processing/BUILD.gn
diff --git a/webrtc/modules/video_processing/BUILD.gn b/webrtc/modules/video_processing/BUILD.gn
index e43c88cbdab0fc61ae8fd525a7bdf43f9a9189f4..7c9391a6d4e9fc60bef8c97737c694c2a78c138b 100644
--- a/webrtc/modules/video_processing/BUILD.gn
+++ b/webrtc/modules/video_processing/BUILD.gn
@@ -98,6 +98,13 @@ if (rtc_build_with_neon) {
 if (rtc_include_tests) {
   rtc_source_set("video_processing_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 = [
       "test/denoiser_test.cc",
     ]