[Sync] Generalize StringOrdinal to handle ordinal_in_parent field

sync/protocol/sync.proto

 // 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.
 //
 // Sync protocol for communication between sync client and server.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 290 matching lines @@
   // If present in Commit updates for the entity, it will be ignored.
   //
   // Available in version 24+.
   //
   // May be returned in GetUpdatesMessage and sent up in CommitMessage.
   //
   optional string client_defined_unique_tag = 23;
 
   // Supplies an ordinal for this item, relative to other items with the
   // same parent.  Ordinals are ordered lexicographically bytewise.
-  // Ordinals must be a least 8 bytes (for backwards compatibility), and
+  // Ordinals must be at least 8 bytes (for backwards compatibility), and
   // must not be all zeroes.
   //
   // Clients should not make sure that each item they know of has a
   // unique ordinal-in-parent.  However, updates from the server might
   // break this invariant.  In that case, among the items with the
   // same ordinal-in-parent, a client should randomly pick one, and
   // then perturb the ordinal-in-parents of all the other ones (within
   // the bounds of the preceding and succeeding ordinal-in-parent)
   // until they're unique; a byte of randomness per item should be
   // more than enough.
@@ skipping 351 matching lines @@
     optional string url                     = 3;
     optional SyncEnums.Action action        = 4 [default = UNKNOWN_ACTION];
 
     // Currently only meaningful if |error_type| is throttled. If this field
     // is absent then the whole client (all datatypes) is throttled.
     repeated int32 error_data_type_ids = 5;
   }
   optional Error error = 13;
 };