Fix error messages for extra files in js2c.py

tools/js2c.py

 #!/usr/bin/env python
 #
 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 423 matching lines @@
     is_debugger = IsDebuggerFile(source)
     result.is_debugger_id.append(is_debugger)
 
     name = os.path.basename(source)[:-3]
     result.names.append(name if not is_debugger else name[:-9])
 
   for extra in extra_files:
     try:
       lines = extra_filters(extra)
     except Error as e:
-      raise Error("In file %s:\n%s" % (source, str(e)))
+      raise Error("In file %s:\n%s" % (extra, str(e)))
 
     result.modules.append(lines)
-    name = os.path.basename(source)[:-3]
+    name = os.path.basename(extra)[:-3]
     result.names.append(name)
 
   return result
 
 
 def BuildMetadata(sources, source_bytes, native_type):
   """Build the meta data required to generate a libaries file.
 
   Args:
     sources: A Sources instance with the prepared sources.
@@ skipping 135 matching lines @@
                       help="writes a JS file output instead of a C file",
                       action="store_true")
 
   args = vars(parser.parse_args())
   JS2C(args["sources.js"], args["extra"] or [], args["out.cc"], args["type"], args["raw"], args["startup_blob"],
        args["js"])
 
 
 if __name__ == "__main__":
   main()