[Findit] Implementing swarming task error detection

appengine/findit/waterfall/trigger_base_swarming_task_pipeline.py

 # 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.
 
 import copy
 import logging
 import time
 
 from common.http_client_appengine import HttpClientAppengine as HttpClient
 from common.pipeline_wrapper import BasePipeline
@@ skipping 150 matching lines @@
         ref_task_id, http_client)
 
     # 2. Update/Overwrite parameters for the re-run.
     iterations_to_rerun = self._GetIterationsToRerun()
 
     new_request = self._CreateNewSwarmingTaskRequest(
         ref_task_id, ref_request, master_name, builder_name, build_number,
         step_name, tests, iterations_to_rerun)
 
     # 3. Trigger a new Swarming task to re-run the failed tests.
-    task_id = swarming_util.TriggerSwarmingTask(new_request, http_client)
+    task_id, error = swarming_util.TriggerSwarmingTask(new_request, http_client)
 
-    # Save the task id.
+    # Update swarming task info.
     swarming_task = self._GetSwarmingTask(*call_args)
     swarming_task.task_id = task_id
     swarming_task.parameters['tests'] = tests
     swarming_task.parameters['iterations_to_rerun'] = iterations_to_rerun
     swarming_task.parameters['ref_name'] = swarming_util.GetTagValue(
         new_request.tags, 'ref_name')
+
+    if error:
+      swarming_task.error = error
+    else:
+      logging.info('A Swarming task was triggered:%s', task_id)
+
     swarming_task.put()
-
-    logging.info('A Swarming task was triggered:%s', task_id)
     return task_id