GN: Tighten up test target visibility + refactorings

webrtc/api/BUILD.gn

Index: webrtc/api/BUILD.gn
diff --git a/webrtc/api/BUILD.gn b/webrtc/api/BUILD.gn
index 71e5243f90336e3f614fd1bf42f739a52ac304d2..d90bb5f7da31d3c53b2692a924c142a53bf19b5c 100644
--- a/webrtc/api/BUILD.gn
+++ b/webrtc/api/BUILD.gn
@@ -230,6 +230,9 @@ if (rtc_include_tests) {
 
   rtc_source_set("rtc_api_unittests") {
     testonly = true
+    if (!is_android && !is_ios) {  # Generated targets makes this check break.

[kjellander_webrtc, 2017/04/21 12:13:59]

What I mean with this is that when building rtc_unittests for Android and iOS,
there's a bunch of extra targets generated by the templates, which has names
that aren't matched by this.
Covering all those would look spammy and ugly here, so I decided it's easier to
just exclude those platforms, since the main benefit of this is to make it clear
where the test is used and to avoid accidental dependencies.

[stefan-webrtc, 2017/04/21 12:28:27]

I think it would be good to describe this in a bit more detail in the comment.

Does it mean these tests won't run on android and ios, or does it just mean that
there will be no visibility restrictions at all?

s/makes/make

[kjellander_webrtc, 2017/04/21 12:48:21]

Done.

+      visibility = [ "//webrtc:rtc_unittests" ]
+    }
     sources = [
       "ortc/mediadescription_unittest.cc",
       "ortc/sessiondescription_unittest.cc",