Make gold plugin download more robust.

build/download_gold_plugin.py

 #!/usr/bin/env python
 # Copyright 2015 the V8 project authors. All rights reserved.
 # 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.
 
 """Script to download LLVM gold plugin from google storage."""
 
 import json
 import os
@@ skipping 39 matching lines @@
     # Bailout if this is not a cfi build.
     print 'Skipping gold plugin download for non-cfi build.'
     return 0
   if (os.path.exists(GOLD_PLUGIN_PATH) and
       update.ReadStampFile().strip() == update.PACKAGE_VERSION):
     # Bailout if clang is up-to-date. This requires the script to be run before
     # the clang update step! I.e. afterwards clang would always be up-to-date.
     print 'Skipping gold plugin download. File present and clang up to date.'
     return 0
 
+  # Make sure this works on empty checkouts (i.e. clang not downloaded yet).
+  if not os.path.exists(LLVM_BUILD_PATH):
+    os.makedirs(LLVM_BUILD_PATH)
+
   targz_name = 'llvmgold-%s.tgz' % CLANG_REVISION
   remote_path = '%s/%s' % (CLANG_BUCKET, targz_name)
 
   os.chdir(LLVM_BUILD_PATH)
 
   # TODO(pcc): Fix gsutil.py cp url file < /dev/null 2>&0
   # (currently aborts with exit code 1,
   # https://github.com/GoogleCloudPlatform/gsutil/issues/289) or change the
   # stdin->stderr redirect in update.py to do something else (crbug.com/494442).
   subprocess.check_call(['python', GSUTIL_PATH,
                          'cp', remote_path, targz_name],
                         stderr=open('/dev/null', 'w'))
   subprocess.check_call(['tar', 'xzf', targz_name])
   os.remove(targz_name)
   return 0
 
 if __name__ == '__main__':
   sys.exit(main())