Use relative paths in GN files.

webrtc/p2p/BUILD.gn

Index: webrtc/p2p/BUILD.gn
diff --git a/webrtc/p2p/BUILD.gn b/webrtc/p2p/BUILD.gn
index f7d59058ba500695f22d4d3317295d68771df8d5..daa2d8498e24221f5c68f5a3f7fb183dc6f4637f 100644
--- a/webrtc/p2p/BUILD.gn
+++ b/webrtc/p2p/BUILD.gn
@@ -170,7 +170,7 @@ if (rtc_include_tests) {
     # 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:rtc_unittests" ]
+      visibility = [ "..:rtc_unittests" ]
     }
     sources = [
       "base/asyncstuntcpsocket_unittest.cc",
@@ -250,7 +250,7 @@ if (rtc_include_tests) {
     # 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:rtc_unittests" ]
+      visibility = [ "..:rtc_unittests" ]
     }
     sources = [
       "stunprober/stunprober_unittest.cc",