Fail with a clear error if the required SDK is not installed.

build/mac/find_sdk.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 """Prints the lowest locally available SDK version greater than or equal to a
 given minimum sdk version to standard output.
 
 Usage:
   python find_sdk.py 10.6  # Ignores SDKs < 10.6
@@ skipping 57 matching lines @@
     print >> sys.stderr, '                                           vvvvvvv'
     print >> sys.stderr, ''
     print >> sys.stderr, \
         'This build requires the %s SDK, but it was not found on your system.' \
         % min_sdk_version
     print >> sys.stderr, \
         'Either install it, or explicitly set mac_sdk in your GYP_DEFINES.'
     print >> sys.stderr, ''
     print >> sys.stderr, '                                           ^^^^^^^'
     print >> sys.stderr, ''
-    return min_sdk_version
+    sys.exit(1)
 
   if options.print_sdk_path:
     print subprocess.check_output(
         ['xcrun', '-sdk', 'macosx' + best_sdk, '--show-sdk-path']).strip()
 
   return best_sdk
 
 
 if __name__ == '__main__':
   if sys.platform != 'darwin':
     raise Exception("This script only runs on Mac")
   print main()
   sys.exit(0)