Override _runner_flags for num_fuzzer.py

This CL ensures that we add the
'--fuzzing' flag to the num_fuzzer script.
Please note that NumFuzzer does not inherit the
StandardTestRunner class but it inherits
BaseTestRunner so we had to override _runner_flags.

Bug: v8:10755
Change-Id: Ifb779ba402106b8f2ce4d0e13090ef2db468a6ae
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2335185
Commit-Queue: Almothana Athamneh <almuthanna@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69241}
diff --git a/tools/testrunner/num_fuzzer.py b/tools/testrunner/num_fuzzer.py
index 7777f4c..e568deb 100755
--- a/tools/testrunner/num_fuzzer.py
+++ b/tools/testrunner/num_fuzzer.py
@@ -117,6 +117,10 @@
   def _get_default_suite_names(self):
     return DEFAULT_SUITES
 
+  def _runner_flags(self):
+    """Extra default flags specific to the test runner implementation."""
+    return ['--fuzzing']
+
   def _get_statusfile_variables(self, options):
     variables = (
         super(NumFuzzer, self)._get_statusfile_variables(options))