Creating new gn arg: enable_all_proguard_optimizations.

build/config/android/rules.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/android/internal_rules.gni")
 import("//build/toolchain/toolchain.gni")
 
 assert(is_android)
 
@@ skipping 1811 matching lines @@
           ":$java_target",  # Generates the jar file.
         ]
       }
     }
 
     if (_proguard_enabled) {
       _proguard_configs = [ _generated_proguard_config ]
       if (defined(invoker.proguard_configs)) {
         _proguard_configs += invoker.proguard_configs
       }
+      assert(_proguard_configs != [])  # Mark as used.
       _proguard_target = "${_template_name}__proguard"
       proguard(_proguard_target) {
         forward_variables_from(invoker,
                                [
                                  "alternative_android_sdk_jar",
                                  "proguard_jar_path",
                                ])
         deps = [
           ":$build_config_target",
           ":$java_target",
@@ skipping 709 matching lines @@
     android_library(target_name) {
       chromium_code = false
       java_files = []
       srcjar_deps = [ ":${_template_name}__protoc_java" ]
       deps = [
         "//third_party/android_protobuf:protobuf_nano_javalib",
       ]
     }
   }
 }