Allow test and unittest_apk GN targets to use proguard

This CL adds proguard arguments to test and unittest_apk GN targets.
This does not change the default behavior for these two targets.

BUG=359249

Review-Url: https://codereview.chromium.org/2000333003
Cr-Commit-Position: refs/heads/master@{#396031}
diff --git a/testing/test.gni b/testing/test.gni
index 78a8a37..f87449f 100644
--- a/testing/test.gni
+++ b/testing/test.gni
@@ -158,6 +158,8 @@
       _apk_specific_vars = [
         "android_manifest",
         "enable_multidex",
+        "proguard_configs",
+        "proguard_enabled",
         "use_default_launcher",
         "write_asset_list",
       ]