Have field ordering for method parameters and response starts at 0.

mojo/public/tools/bindings/pylib/mojom/generate/pack.py

 # Copyright 2013 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 module as mojom
 
 # This module provides a mechanism for determining the packed order and offsets
 # of a mojom.Struct.
 #
 # ps = pack.PackedStruct(struct)
@@ skipping 63 matching lines @@
   def __init__(self, struct):
     self.struct = struct
     self.packed_fields = []
 
     # No fields.
     if (len(struct.fields) == 0):
       return
 
     # Start by sorting by ordinal.
     src_fields = []
-    ordinal = 1
+    ordinal = 0
     for field in struct.fields:
       if field.ordinal is not None:
         ordinal = field.ordinal
       src_fields.append(PackedField(field, ordinal))
       ordinal += 1
     src_fields.sort(key=lambda field: field.ordinal)
 
     src_field = src_fields[0]
     src_field.offset = 0
     src_field.bit = 0
@@ skipping 45 matching lines @@
     limit_of_previous_field = packed_field.offset + packed_field.size
 
   for i in xrange(limit_of_previous_field, len(bytes)):
     bytes[i].is_padding = True
 
   for byte in bytes:
     # A given byte cannot both be padding and have a fields packed into it.
     assert not (byte.is_padding and byte.packed_fields)
 
   return bytes