sync: Implement per-type update processing

sync/test/engine/mock_connection_manager.cc

Index: sync/test/engine/mock_connection_manager.cc
diff --git a/sync/test/engine/mock_connection_manager.cc b/sync/test/engine/mock_connection_manager.cc
index 2290fea35cf2f281853637a0bb706e932b451ae0..624e02218822a9c2fc9509f10280222fbabb5915 100644
--- a/sync/test/engine/mock_connection_manager.cc
+++ b/sync/test/engine/mock_connection_manager.cc
@@ -533,12 +533,10 @@ void MockConnectionManager::ProcessGetUpdates(
   std::string token = response->get_updates().new_progress_marker(0).token();
   response->mutable_get_updates()->clear_new_progress_marker();
   for (int i = 0; i < gu.from_progress_marker_size(); ++i) {
-    if (gu.from_progress_marker(i).token() != token) {
-      sync_pb::DataTypeProgressMarker* new_marker =
-          response->mutable_get_updates()->add_new_progress_marker();
-      new_marker->set_data_type_id(gu.from_progress_marker(i).data_type_id());
-      new_marker->set_token(token);
-    }
+    sync_pb::DataTypeProgressMarker* new_marker =

[Nicolas Zea, 2013/10/25 21:04:41]

what is this change for?

[rlarocque, 2013/10/25 22:29:47]

This uses a little-known feature in the sync protocol.  Apparently, if the
progress markers for a given type are not present in the response, the client is
supposed to just accept that and leave its current progress markers as is.

This feature doesn't make a lot of sense these days, and our real server never
uses it, so I've decided to deprecate it.

This code implements a sort of optimization where the progress marker is not
sent in the response if it is equal to what came up in the request.  I presume
some old servers used to do this.

+        response->mutable_get_updates()->add_new_progress_marker();
+    new_marker->set_data_type_id(gu.from_progress_marker(i).data_type_id());
+    new_marker->set_token(token);
   }
 
   // Fill the keystore key if requested.