Followup to 'Scripts to upload and update the mac toolchain.'

build/mac_toolchain.py

 #!/usr/bin/env python
 # 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.
 
 """Download necessary mac toolchain files under certain conditions.  If
 xcode-select is already set and points to an external folder
 (e.g. /Application/Xcode.app), this script only runs if the GYP_DEFINE
 |force_mac_toolchain| is set.  To override the values in
 |TOOLCHAIN_REVISION|-|TOOLCHAIN_SUB_REVISION| below, GYP_DEFINE
@@ skipping 22 matching lines @@
 
 BASE_DIR = os.path.abspath(os.path.dirname(__file__))
 TOOLCHAIN_BUILD_DIR = os.path.join(BASE_DIR, 'mac_files', 'Xcode.app')
 STAMP_FILE = os.path.join(BASE_DIR, 'mac_files', 'toolchain_build_revision')
 TOOLCHAIN_URL = 'gs://chrome-mac-sdk/'
 
 
 def GetToolchainDirectory():
   if sys.platform == 'darwin' and not UseLocalMacSDK():
     return TOOLCHAIN_BUILD_DIR
+  else:
+    return None
 
 
 def ReadStampFile():
   """Return the contents of the stamp file, or '' if it doesn't exist."""
   try:
     with open(STAMP_FILE, 'r') as f:
       return f.read().rstrip()
   except IOError:
     return ''
 
@@ skipping 92 matching lines @@
     print 'Toolchain %s unpacked.' % toolchain_revision
     WriteStampFile(toolchain_revision)
     return 0
   except:
     print 'Failed to download toolchain %s.' % toolchain_file
     print 'Exiting.'
     return 1
 
 if __name__ == '__main__':
   sys.exit(main())