[android] Write a runner script to the top-level output dir for gtests.

build/config/android/internal_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_overrides/build.gni")
 import("//build/config/android/config.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/sanitizers/sanitizers.gni")
@@ skipping 597 matching lines @@
           "--apk-under-test-incremental-install-script",
           "@FileArg($_rebased_apk_under_test_build_config:deps_info:incremental_install_script_path)",
         ]
       }
       test_runner_args += [ "--fast-local-dev" ]
     }
     if (_device_test && is_asan) {
       test_runner_args += [ "--tool=asan" ]
     }
 
-    generated_script = "$root_build_dir/bin/run_${_test_name}"
+    if (defined(invoker.generated_script)) {
+      assert(_test_name != "" || true)  # Mark _test_name as used.
+      generated_script = invoker.generated_script
+    } else {
+      generated_script = "$root_build_dir/bin/run_${_test_name}"
+    }
     outputs = [
       generated_script,
     ]
     data += [ generated_script ]
 
     args = [
       "--depfile",
       rebase_path(depfile, root_build_dir),
       "--script-output-path",
       rebase_path(generated_script, root_build_dir),
@@ skipping 2218 matching lines @@
         rebase_path(root_build_dir, root_build_dir),
         "--packed-libraries-dir",
         rebase_path(_packed_libraries_dir, root_build_dir),
         "--libraries=${invoker.libraries_filearg}",
         "--filelistjson",
         rebase_path(invoker.file_list_json, root_build_dir),
       ]
     }
   }
 }