Do not crash build if Java is not installed

tools/utils.py

 # Copyright (c) 2012, 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 file contains a set of utilities functions used by other Python-based
 # scripts.
 
 import commands
 import os
 import platform
@@ skipping 282 matching lines @@
 
 
 def ConfigureJava():
   java_home = '/usr/libexec/java_home'
   if os.path.exists(java_home):
     proc = subprocess.Popen([java_home, '-v', '1.6+'],
                             stdout=subprocess.PIPE,
                             stderr=subprocess.PIPE)
     (stdout, stderr) = proc.communicate()
     if proc.wait() != 0:
-      raise ToolError('non-zero exit code from ' + java_home)
+      return None
     new = stdout.strip()
     current = os.getenv('JAVA_HOME', default=new)
     if current != new:
       sys.stderr.write('Please set JAVA_HOME to %s\n' % new)
       os.putenv('JAVA_HOME', new)
 
 
 def Daemonize():
   """
   Create a detached background process (daemon). Returns True for
@@ skipping 80 matching lines @@
 
 def DartSdkBinary():
   tools_dir = os.path.dirname(os.path.realpath(__file__))
   dart_binary_prefix = os.path.join(tools_dir, '..', 'sdk' , 'bin')
   return os.path.join(dart_binary_prefix, 'dart')
 
 
 if __name__ == "__main__":
   import sys
   Main(sys.argv)