[Sync] Server side update the protocol version, because server side adding a...

[Sync] Server side update the protocol version, because server side adding a error type, which is partial_faulure. we already support this error type, so this change just need to update default version.

BUG=470736

Review URL: https://codereview.chromium.org/1030293002

Cr-Commit-Position: refs/heads/master@{#322329}

sync/protocol/sync.proto

@@ -714,7 +714,7 @@ message DataTypeContext {
 
 message ClientToServerMessage {
   required string share = 1;
-  optional int32 protocol_version = 2 [default = 42];
+  optional int32 protocol_version = 2 [default = 43];
   enum Contents {
     COMMIT = 1;
     GET_UPDATES = 2;