[RTS] Add back in RTS support to GNI

- Add use_rts bool flag to ensure that a .filter
file exists or creates a dummy file while waiting
for the file to be written.

RTS = Regression Test Selection
Re-land of https://crrev.com/c/4859614

Bug: 375000947
Change-Id: I425e0891ac895ae043855e0372be8a0e43a96f0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5954865
Reviewed-by: Dirk Pranke <dpranke@google.com>
Reviewed-by: Struan Shrimpton <sshrimp@google.com>
Commit-Queue: Tony Seaward <seawardt@google.com>
Cr-Commit-Position: refs/heads/main@{#1374746}


CrOS-Libchrome-Original-Commit: 37c51bc8d9cbbd11ef6cb8d872b82080dab839df

Author: SeawardT

build/add_rts_filters.py

@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+# Copyright 2024 The Chromium Authors
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+"""Creates a dummy RTS filter file if a real ones do not exist yet.
+  Real filter files are generated for suites with skippable tests.
+  Not every test suite will have filter data to use and therefore
+  no filter file will be created. This ensures that a file exists
+  to avoid file not found errors. The files will contain no skippable
+  tests, so there is no effect.
+
+  Implementation uses try / except because the filter files are written
+  relatively close to when this code creates the dummy files.
+
+  The following type of implementation would have a race condition:
+  if not os.path.isfile(filter_file):
+    open(filter_file, 'w') as fp:
+      fp.write('*')
+"""
+import errno
+import os
+import sys
+
+
+def main():
+  filter_file = sys.argv[1]
+  # '*' is a dummy that means run everything
+  write_filter_file(filter_file, '*')
+
+
+def write_filter_file(filter_file, filter_string):
+  directory = os.path.dirname(filter_file)
+  try:
+    os.makedirs(directory)
+  except OSError as err:
+    if err.errno == errno.EEXIST:
+      pass
+    else:
+      raise
+  try:
+    fp = os.open(filter_file, os.O_CREAT | os.O_EXCL | os.O_WRONLY)
+  except OSError as err:
+    if err.errno == errno.EEXIST:
+      pass
+    else:
+      raise
+  else:
+    with os.fdopen(fp, 'w') as file_obj:
+      file_obj.write(filter_string)
+
+
+if __name__ == '__main__':
+  sys.exit(main())