Check for existence of logdog binary and logcat source before uploading.

build/android/test_wrapper/logdog_wrapper.py

 #!/usr/bin/env python
 # Copyright 2016 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.
 
 """Wrapper for adding logdog streaming support to swarming tasks."""
 
 import argparse
 import logging
 import os
@@ skipping 54 matching lines @@
     args.prefix = args.prefix.replace('${SWARMING_TASK_ID}',
                                       os.environ.get('SWARMING_TASK_ID'))
   url = CreateUrl('luci-logdog.appspot.com', args.project, args.prefix,
                   args.name)
   logdog_cmd = [args.logdog_bin_cmd, '-project', args.project,
                 '-output', 'logdog,host=%s' % args.logdog_server,
                 '-prefix', args.prefix,
                 '-service-account-json', args.service_account_json,
                 'stream', '-source', args.source,
                 '-stream', '-name=%s' % args.name]
-  if os.path.exists(args.logdog_bin_cmd):
+
+  if not os.path.exists(args.logdog_bin_cmd):
+    logging.error(
+        'Logfog binary %s unavailable. Unable to upload logcats.',
+        args.logdog_bin_cmd)
+  elif not os.path.exists(args.source):
+    logging.error(
+        'Logcat sources not found at %s. Unable to upload logcats.',
+        args.source)
+  else:
     subprocess.call(logdog_cmd)
     logging.info('Logcats are located at: %s', url)
   return result
 
 
 if __name__ == '__main__':
   sys.exit(main())