GN: Only define UNIT_TEST in direct gtest deps

build/secondary/testing/gtest/BUILD.gn

Index: build/secondary/testing/gtest/BUILD.gn
diff --git a/build/secondary/testing/gtest/BUILD.gn b/build/secondary/testing/gtest/BUILD.gn
index eb8604dc153a183b5b44ca925f2a066d7758ac58..f7c1e0d7208c9e49f7dc652d03800293de449f11 100644
--- a/build/secondary/testing/gtest/BUILD.gn
+++ b/build/secondary/testing/gtest/BUILD.gn
@@ -9,7 +9,6 @@ config("gtest_config") {
   ]
 
   defines = [
-    "UNIT_TEST",
 
     # In order to allow regex matches in gtest to be shared between Windows
     # and other systems, we tell gtest to always use it's internal engine.
@@ -54,6 +53,11 @@ config("gtest_config") {
   }
 }
 
+config("gtest_direct_config") {
+  visibility = ":*"
+  defines = [ "UNIT_TEST" ]
+}
+
 static_library("gtest") {
   sources = [
     "include/gtest/gtest-death-test.h",
@@ -100,6 +104,7 @@ static_library("gtest") {
   include_dirs = [ "." ]
 
   all_dependent_configs = [ ":gtest_config" ]
+  direct_dependent_configs = [ ":gtest_direct_config" ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]