Fix a typo in JSON Schema Compiler's help prompt.

tools/json_schema_compiler/compiler.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.
 """Generator for C++ structs from api json files.
 
 The purpose of this tool is to remove the need for hand-written code that
 converts to and from base::Value types when receiving javascript api calls.
 Originally written for generating code for extension apis. Reference schemas
 are in chrome/common/extensions/api.
@@ skipping 112 matching lines @@
     output_code += [filename, '', code, '']
 
   return '\n'.join(output_code)
 
 if __name__ == '__main__':
   parser = optparse.OptionParser(
       description='Generates a C++ model of an API from JSON schema',
       usage='usage: %prog [option]... schema')
   parser.add_option('-r', '--root', default='.',
       help='logical include root directory. Path to schema files from specified'
-      'dir will be the include path.')
+      ' dir will be the include path.')
   parser.add_option('-d', '--destdir',
       help='root directory to output generated files.')
   parser.add_option('-n', '--namespace', default='generated_api_schemas',
       help='C++ namespace for generated files. e.g extensions::api.')
   parser.add_option('-g', '--generator', default=GENERATORS[0],
       choices=GENERATORS,
       help='The generator to use to build the output code. Supported values are'
       ' %s' % GENERATORS)
   parser.add_option('-D', '--dart-overrides-dir', dest='dart_overrides_dir',
       help='Adds custom dart from files in the given directory (Dart only).')
 
   (opts, filenames) = parser.parse_args()
 
   if not filenames:
     sys.exit(0) # This is OK as a no-op
 
   # Unless in bundle mode, only one file should be specified.
   if opts.generator != 'cpp-bundle' and len(filenames) > 1:
     # TODO(sashab): Could also just use filenames[0] here and not complain.
     raise Exception(
         "Unless in bundle mode, only one file can be specified at a time.")
 
   result = GenerateSchema(opts.generator, filenames, opts.root, opts.destdir,
                           opts.namespace, opts.dart_overrides_dir)
   if not opts.destdir:
     print result