[Findit] Catch ValueError when get swarming result.

appengine/findit/waterfall/swarming_util.py

 # Copyright 2015 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 base64
 from collections import defaultdict
 import json
+import logging
 import urllib
 import zlib
 
 from google.appengine.ext import ndb
 
 from common import auth_util
 from model.wf_step import WfStep
 from waterfall import waterfall_config
 from waterfall.swarming_task_request import SwarmingTaskRequest
 
@@ skipping 227 matching lines @@
   else the log would be in content so use it directly.
   """
   json_content = json.loads(output_json_content)
   output_json_url = json_content.get('url')
   if output_json_url:
     get_content = _SendRequestToServer(output_json_url, http_client)
   elif json_content.get('content'):
     get_content = base64.b64decode(json_content['content'])
   else:  # pragma: no cover
     get_content = None  # Just for precausion.
-  return json.loads(zlib.decompress(get_content)) if get_content else None
-
+  try:
+    return json.loads(zlib.decompress(get_content)) if get_content else None
+  except ValueError:  # pragma: no cover
+    logging.info(
+        'swarming result is invalid: %s' % zlib.decompress(get_content))
+    return None
 
 def _DownloadTestResults(isolated_data, http_client):
   """Downloads the output.json file and returns the json object."""
   # First POST request to get hash for the output.json file.
   content = _FetchOutputJsonInfoFromIsolatedServer(
       isolated_data, http_client)
   if not content:
     return None
   output_json_hash = _GetOutputJsonHash(content)
   if not output_json_hash:
@@ skipping 76 matching lines @@
   shard_results = []
   for isolated_data in list_isolated_data:
     output_json = _DownloadTestResults(isolated_data, http_client)
     if not output_json:
       return None
     shard_results.append(output_json)
 
   if len(list_isolated_data) == 1:
     return shard_results[0]
   return _MergeSwarmingTestShards(shard_results)