Fix some minor bugs related to imports in the new mojom bindings generator.

mojo/public/tools/bindings/run_code_generators.py

 #!/usr/bin/env python
 # Copyright 2015 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.
 #
 # This script accepts the output of version 2 of the mojom parser and uses that
 # data to invoke the code generators.
 #
 # This script is not related mojom_bindings_generator.py (which is part of v1
 # of the mojom parser pipeline).
@@ skipping 111 matching lines @@
 
   The path provided for the various modules is the absolute path to the mojom
   file which the module represents. But the generators expect the path to be
   relative to the root of the source tree.
 
   Args:
     module: {module.Module} whose path is to be updated.
     abs_root: {str} absolute path to the root of the source tree.
   """
   module.path = os.path.relpath(module.path, src_root_path)
+  if not hasattr(module, 'imports'):
+    return
   for import_dict in module.imports:
     FixModulePath(import_dict['module'], src_root_path)
 
 
 def main():
   args, remaining_args = _ParseCLIArgs()
 
   if args.file_graph == '-':
     fp = sys.stdin
   else:
@@ skipping 14 matching lines @@
       if hasattr(generator_module, 'GENERATOR_PREFIX'):
         prefix = '--' + generator_module.GENERATOR_PREFIX + '_'
         filtered_args = [arg for arg in remaining_args
                          if arg.startswith(prefix)]
 
       generator.GenerateFiles(filtered_args)
 
 
 if __name__ == "__main__":
   sys.exit(main())