GN: Use rtc_include_tests variable to exclude tests.

webrtc/base/BUILD.gn

Index: webrtc/base/BUILD.gn
diff --git a/webrtc/base/BUILD.gn b/webrtc/base/BUILD.gn
index 7d2035db862e81b8b3d7cb3462719f7efe99acef..92aa2f6d3d3e539f1f1fcd974b25658194419b9b 100644
--- a/webrtc/base/BUILD.gn
+++ b/webrtc/base/BUILD.gn
@@ -632,8 +632,7 @@ source_set("gtest_prod") {
   ]
 }
 
-# There's no point processing WebRTC standalone tests in a Chromium build.
-if (!build_with_chromium) {
+if (!rtc_include_tests) {
   config("rtc_base_test_utils_exported_config") {
     defines = [ "GTEST_RELATIVE_PATH" ]
   }