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

tools/json_schema_compiler/idl_schema.py

Index: tools/json_schema_compiler/idl_schema.py
diff --git a/tools/json_schema_compiler/idl_schema.py b/tools/json_schema_compiler/idl_schema.py
index 72e4d13b4fd67c9464343d40f40b6c75d3a1e937..89bb8816b0c82f9237e4f14ca287861c5a036d60 100644
--- a/tools/json_schema_compiler/idl_schema.py
+++ b/tools/json_schema_compiler/idl_schema.py
@@ -469,8 +469,14 @@ 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)