Fix make_version.py in cases where we cant get revision info

runtime/tools/make_version.py

 # 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.
 #
 # This python script creates a version string in a C++ file.
 
 import os
 import sys
 import subprocess
 import platform
 import getpass
 from os.path import join
 import time
 from optparse import OptionParser
 
 def getVersionPart(version_file, part):
   proc = subprocess.Popen(['awk',
                            '$1 == "%s" {print $2}' % (part),
                            version_file],
                           stdout=subprocess.PIPE,
                           stderr=subprocess.STDOUT)
   return proc.communicate()[0].split('\n')[0]
 
 def getRevision():
   is_svn = True
   if os.path.exists('.svn'):
     cmd = ['svn', 'info']
   else:
     cmd = ['git', 'svn', 'info']
-  proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
-  return proc.communicate()[0].split('\n')[4].split(' ')[1]
-  
+  try:
+    proc = subprocess.Popen(cmd,
+                            stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+    return proc.communicate()[0].split('\n')[4].split(' ')[1]
+  except Exception:
+    # If we can't get any revision info (due to lack of tooling) return ''.
+    return ''
+
+
 def makeVersionString(version_file):
   id = platform.system()
   if id == 'Windows' or id == 'Microsoft':
     return '0.0.0.0'
   major = getVersionPart(version_file, 'MAJOR')
   minor = getVersionPart(version_file, 'MINOR')
   build = getVersionPart(version_file, 'BUILD')
   patch = getVersionPart(version_file, 'PATCH')
   revision = getRevision()
   user = getpass.getuser()
@@ skipping 42 matching lines @@
 
     return 0
   except Exception, inst:
     sys.stderr.write('make_version.py exception\n')
     sys.stderr.write(str(inst))
     sys.stderr.write('\n')
     return -1
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))