Migrate WebRTC test infra to ABSL_FLAG.

This is the last CL required to migrate WebRTC to ABSL_FLAG, rtc::Flag
will be removed soon after this one lands.

Bug: webrtc:10616
Change-Id: I2807cec39e28a2737d2c49e2dc23f2a6f98d08f0
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/145727
Reviewed-by: Tommi <tommi@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28606}
diff --git a/tools_webrtc/gtest_parallel_wrapper_test.py b/tools_webrtc/gtest_parallel_wrapper_test.py
index e5447e3..5d436aa 100755
--- a/tools_webrtc/gtest_parallel_wrapper_test.py
+++ b/tools_webrtc/gtest_parallel_wrapper_test.py
@@ -148,7 +148,7 @@
           '--output_dir=' + output_dir, '--dump_json_test_results=SOME_DIR',
           'some_test', '--', '--test_artifacts_dir=' + expected_artifacts_dir,
           '--some_flag=some_value', '--another_flag',
-          '--isolated-script-test-perf-output=SOME_OTHER_DIR', '--foo=bar',
+          '--isolated_script_test_perf_output=SOME_OTHER_DIR', '--foo=bar',
           '--baz'
       ])
       self.assertEqual(result.gtest_parallel_args, expected)