Creating new gn arg: enable_all_proguard_optimizations.

build/config/android/rules.gni

Index: build/config/android/rules.gni
diff --git a/build/config/android/rules.gni b/build/config/android/rules.gni
index a6cc4fe6edee9c2581c5260ad2f11295e97caa9f..d4a3bb0c4be7d8fe294369549b5f53ec0bd52ac2 100644
--- a/build/config/android/rules.gni
+++ b/build/config/android/rules.gni
@@ -1829,6 +1829,7 @@ if (enable_java_templates) {
       if (defined(invoker.proguard_configs)) {
         _proguard_configs += invoker.proguard_configs
       }
+      assert(_proguard_configs != [])  # Mark as used.
       _proguard_target = "${_template_name}__proguard"
       proguard(_proguard_target) {
         forward_variables_from(invoker,
@@ -1841,6 +1842,9 @@ if (enable_java_templates) {
           ":$java_target",
           ":$process_resources_target",
         ]
+        if (!enable_all_proguard_optimizations) {
+          _proguard_configs += [ "//testing/android/proguard_for_test.flags" ]
+        }
         inputs = [
                    _build_config,
                    _jar_path,