Updating android_aar_prebuilt rule to prevent unneeded args if the res folder is empty.

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.
 
 # Do not add any imports to non-//build directories here.
 # Some projects (e.g. V8) do not have non-build directories DEPS'ed in.
 import("//build/config/android/config.gni")
 import("//build/config/android/internal_rules.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/dcheck_always_on.gni")
@@ skipping 2795 matching lines @@
     # Create the android_resources target for resources.
     if (_scanned_files.resources != [] || _scanned_files.has_r_text_file) {
       _res_target_name = "${target_name}__res"
       android_resources(_res_target_name) {
         forward_variables_from(invoker, [ "deps" ])
         if (!defined(deps)) {
           deps = []
         }
         deps += [ ":$_unpack_target_name" ]
         resource_dirs = []
-        generated_resource_dirs = [ "${_output_path}/res" ]
-        generated_resource_files =
-            rebase_path(_scanned_files.resources, "", _output_path)
+        if (_scanned_files.resources != []) {
+          generated_resource_dirs = [ "${_output_path}/res" ]
+          generated_resource_files =
+              rebase_path(_scanned_files.resources, "", _output_path)
+        }
         android_manifest_dep = ":$_unpack_target_name"
         android_manifest = "${_output_path}/AndroidManifest.xml"
         if (_scanned_files.has_r_text_file) {
           r_text_file = "${_output_path}/R.txt"
         }
         v14_skip = true
       }
     }
 
     # Create android_java_prebuilt target for extra jars within jars/.
@@ skipping 64 matching lines @@
         # because in practice they seem to contain classes required to be in the
         # classpath.
         deps += _subjar_targets
       }
       if (defined(_res_target_name)) {
         deps += [ ":$_res_target_name" ]
       }
     }
   }
 }