Add global presubmit that JSON and IDL files can be parsed.

tools/json_schema_compiler/idl_schema.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.
 
 import itertools
 import json
 import os.path
 import re
 import sys
@@ skipping 451 matching lines @@
   idl = idl_parser.IDLParser().ParseData(contents, filename)
   idl_schema = IDLSchema(idl)
   return idl_schema.process()
 
 
 def Main():
   '''
   Dump a json serialization of parse result for the IDL files whose names
   were passed in on the command line.
   '''
-  for filename in sys.argv[1:]:
-    schema = Load(filename)
+  if len(sys.argv) > 1:
+    for filename in sys.argv[1:]:
+      schema = Load(filename)
+      print json.dumps(schema, indent=2)
+  else:
+    contents = sys.stdin.read()
+    idl = idl_parser.IDLParser().ParseData(contents, '<stdin>')
+    schema = IDLSchema(idl).process()
     print json.dumps(schema, indent=2)
 
 
 if __name__ == '__main__':
   Main()