Made get_archive.py resilient to 403 forbidden errors.

tools/get_archive.py

 #!/usr/bin/env python
 #
 # Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # Gets or updates a DumpRenderTree (a nearly headless build of chrome). This is
 # used for running browser tests of client applications.
 
 import json
@@ skipping 142 matching lines @@
       foundURL = False
       while not foundURL:
         # Test to ensure this URL exists because the dartium-archive builds can
         # have unusual numbering (a range of CL numbers) sometimes.
         result, out = Gsutil('ls', permanent_prefix % {'osname' : osname,
             'num1': '*', 'num2': revision_num })
         if result == 0:
           # First try to find one with the the second number the same as the
           # requested number.
           latest = out.split()[0]
-          foundURL = True
+          # Now test that the permissions are correct so you can actually
+          # download it.
+          temp_dir = tempfile.mkdtemp()
+          temp_zip = os.path.join(temp_dir, 'foo.zip')
+          returncode, out = Gsutil('cp', latest, 'file://' + temp_zip)
+          if returncode == 0:
+            foundURL = True
+          else:
+            # Unable to download this item (most likely because something went
+            # wrong on the upload and the permissions are bad). Keep looking for
+            # a different URL.
+            revision_num = int(revision_num) - 1
+          shutil.rmtree(temp_dir)
         else:
           # Now try to find one with a nearby CL num.
           revision_num = int(revision_num) - 1
           if revision_num <= 0:
             TooEarlyError()
     return latest
     
   GetFromGsutil(name, directory, version_file, latest_pattern, osdict, 
                   FindPermanentUrl, revision_num)
 
@@ skipping 154 matching lines @@
   elif positional[0] == 'drt':
     GetDartiumRevision('DumpRenderTree', DRT_DIR, DRT_VERSION,
                          DRT_LATEST_PATTERN, DRT_PERMANENT_PATTERN,
                          args.revision)
   else:
     print ('Please specify the target you wish to download from Google Storage '
         '("drt", "dartium", "chromedriver", or "sdk")')
 
 if __name__ == '__main__':
   sys.exit(main())