ci: verify chromedriver (#21993)

* initial pass

* better

* even better

* ci

* add chromedriver to build step

* add chromedriver to other build step

* persist chromedriver for tests

* appveyor test

* correct sys.platform names

* chromedriver-path -> build-dir

script/verify-chromedriver.py

@@ -0,0 +1,61 @@
+#!/usr/bin/env python
+
+from __future__ import print_function
+
+import argparse
+import os
+import re
+import shlex
+import subprocess
+import sys
+import time
+
+SOURCE_ROOT = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
+
+
+def main():
+  args = parse_args()
+
+  chromedriver_name = {
+    'darwin': 'chromedriver',
+    'win32': 'chromedriver.exe',
+    'linux2': 'chromedriver'
+}
+
+  chromedriver_path = os.path.join(
+    args.source_root, args.build_dir, chromedriver_name[sys.platform])
+  proc = subprocess.Popen([chromedriver_path],
+                          stdout=subprocess.PIPE, universal_newlines=True)
+  try:
+    output = proc.stdout.readline()
+  except KeyboardInterrupt:
+    returncode = 0
+  finally:
+    proc.terminate()
+
+  returncode = 0
+  match = re.search(
+    '^Starting ChromeDriver [0-9]+.[0-9]+.[0-9]+.[0-9]+ .* on port [0-9]+$', output)
+
+  if match == None:
+    returncode = 1
+
+  if returncode == 0:
+    print('ok ChromeDriver is able to be initialized.')
+
+  return returncode
+
+
+def parse_args():
+    parser=argparse.ArgumentParser(description='Test ChromeDriver')
+    parser.add_argument('--source-root',
+                        default=SOURCE_ROOT,
+                        required=False)
+    parser.add_argument('--build-dir',
+                        default=None,
+                        required=True)
+    return parser.parse_args()
+
+
+if __name__ == '__main__':
+    sys.exit(main())