sync: Enable typed tombstones commits

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 674 matching lines @@
   // The type this context is associated with.
   optional int32 data_type_id = 1;
   // The context for the datatype.
   optional bytes context = 2;
   // The version of the context.
   optional int64 version = 3;
 }
 
 message ClientToServerMessage {
   required string share = 1;
-  optional int32 protocol_version = 2 [default = 32];
+  optional int32 protocol_version = 2 [default = 33];

[haitaol1, 2014/05/19 21:59:12]

Do you have to change this? How is this used on server?

[rlarocque, 2014/05/19 22:14:57]

This is used to tell the server when semantics for certain fields have changed. 
This way it can throw an error if (protocol_version >= 33 && GetModelType() ==
UNSPECIFIED).

Technically, this is bad protobuf hygiene.  Protobufs are not supposed to rely
on version numbers.  There is a "right" solution where we would not need to use
version numbers.  It would be a lot of work to implement, and it would waste a
few bytes.  I doubt I could convince anyone to implement it that way.

   enum Contents {
     COMMIT = 1;
     GET_UPDATES = 2;
     AUTHENTICATE = 3;
     CLEAR_DATA = 4;
   }
 
   required Contents message_contents = 3;
   optional CommitMessage commit = 4;
   optional GetUpdatesMessage get_updates = 5;
@@ skipping 241 matching lines @@
     // 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;
 
   // The new per-client state for this client. If set, should be persisted and
   // sent with any subsequent ClientToServerMessages.
   optional ChipBag new_bag_of_chips = 14;
 };