Fix a couple minor typos in auto_bisect.

tools/auto_bisect/fetch_build.py

 # Copyright 2014 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.
 
 """This module contains functions for fetching and extracting archived builds.
 
 The builds may be stored in different places by different types of builders;
 for example, builders on tryserver.chromium.perf stores builds in one place,
 while builders on chromium.linux store builds in another.
 
@@ skipping 278 matching lines @@
     """Returns the directory name to download builds from."""
     return self._extra_src.GetArchiveDirectory()
 
   def GetBuilderName(self):
     """Returns the builder name extra source."""
     return self._extra_src.GetBuilderName()
 
 
 def BuildIsAvailable(bucket_name, remote_path):
   """Checks whether a build is currently archived at some place."""
-  logging.info('Checking existance: gs://%s/%s' % (bucket_name, remote_path))
+  logging.info('Checking existence: gs://%s/%s' % (bucket_name, remote_path))
   try:
     exists = cloud_storage.Exists(bucket_name, remote_path)
     logging.info('Exists? %s' % exists)
     return exists
   except cloud_storage.CloudStorageError:
     return False
 
 
 def FetchFromCloudStorage(bucket_name, source_path, destination_dir):
   """Fetches file(s) from the Google Cloud Storage.
@@ skipping 151 matching lines @@
     print 'Build is not available.'
     return 1
 
   FetchFromCloudStorage(bucket_name, remote_path, args.output_dir)
   print 'Build has been downloaded to and extracted in %s.' % args.output_dir
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(Main(sys.argv))