Enable NativeActivity based Android tests.

testing/test.gni

Index: testing/test.gni
diff --git a/testing/test.gni b/testing/test.gni
index c01306c644880a3b574cda10aec1445640e51451..3596bbf710325b00172140a2eb8631d209a7c919 100644
--- a/testing/test.gni
+++ b/testing/test.gni
@@ -63,6 +63,7 @@ template("_gen_isolate") {
 # set.
 # Variable:
 #   use_raw_android_executable: Use executable() rather than android_apk().
+#   use_native_activity: Test implements ANativeActivity_onCreate().
 template("test") {
   if (is_android) {
     import("//build/config/android/config.gni")
@@ -160,6 +161,7 @@ template("test") {
         "enable_multidex",
         "use_default_launcher",
         "write_asset_list",
+        "use_native_activity",
       ]
       shared_library(_library_target) {
         # Configs will always be defined since we set_defaults in BUILDCONFIG.gn.