Initializing upload_failed to prevent program initialization failure

There is a case where no benchmarks could be uploading perf results
from a shard (ie they are all disabled).

Bug: 842145
Change-Id: Iea52461dee8e8a7c4475396d9af9f0339cdfaf3e
Reviewed-on: https://chromium-review.googlesource.com/1066080Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#560311}

tools/perf/process_perf_results.py

@@ -253,6 +253,7 @@ def _handle_perf_results(
     logdog_dict = {}
     logdog_stream = None
     logdog_label = 'Results Dashboard'
+    upload_fail = False
     with oauth_api.with_access_token(service_account_file) as oauth_file:
       for directory in benchmark_directory_list:
         benchmark_name = _get_benchmark_name(directory)