sync: Enable typed tombstones commits

sync/protocol/sync.proto

Index: sync/protocol/sync.proto
diff --git a/sync/protocol/sync.proto b/sync/protocol/sync.proto
index 1e9b66ab9b52e7cb37ff32d75240d84de0011cc3..276824272fe2f7835fa37389243dc885f5b99907 100644
--- a/sync/protocol/sync.proto
+++ b/sync/protocol/sync.proto
@@ -692,7 +692,7 @@ message DataTypeContext {
 
 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;