Don't pass "-b" to gsutil when downloading go tool binaries.

tools/go/download.py

 #!/usr/bin/python
 # 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.
 
 """
 Downloads Go binaries from Google Cloud Storage and extracts them to
 INSTALL_DIR, updating INSTALL_DIR/VERSION stamp file with current version.
 Does nothing if INSTALL_DIR/VERSION is already up to date.
 """
@@ skipping 44 matching lines @@
 def InstallGoBinaries(version):
   """Downloads zipped go binaries from Google Cloud Storage and extracts them,
      stamping current version."""
 
   # Remove current installation.
   if os.path.exists(INSTALL_DIR):
     shutil.rmtree(INSTALL_DIR)
   os.mkdir(INSTALL_DIR)
   # Download go tool binaries from GCS.
   archive_path = os.path.join(INSTALL_DIR, 'go.tar.gz')
-  download_cmd = ['python', GSUTIL_PATH, '-b', 'cp',
+  download_cmd = ['python', GSUTIL_PATH, 'cp',
                   'gs://mojo/go/tool/%s.tar.gz' % version,
                   archive_path]
   if not RunCommand(download_cmd):
     print ('WARNING: Failed to download Go tool binaries.')
     return
 
   print "Extracting Go binaries."
   with tarfile.open(archive_path) as arch:
     arch.extractall(INSTALL_DIR)
   os.remove(archive_path)
   # Write version as the last step.
   with open(os.path.join(INSTALL_DIR, VersionFileName()), 'w+') as f:
     f.write('%s\n' % version)
 
 def main():
   # Read latest version.
   version = ''
   with open(os.path.join(THIS_DIR, VersionFileName())) as f:
     version = f.read().strip()
   # Return if installed binaries are up to date.
   if version == GetInstalledVersion():
     return
   InstallGoBinaries(version)
 
 if __name__ == '__main__':
   sys.exit(main())