[Sync] Add full history sync experiment

sync/internal_api/sync_manager_impl.cc

Index: sync/internal_api/sync_manager_impl.cc
diff --git a/sync/internal_api/sync_manager_impl.cc b/sync/internal_api/sync_manager_impl.cc
index 618039c9ec1b5f256411990cedb73fe130b179b2..65e2a47645f054a253d6d1f32777c6017c551e44 100644
--- a/sync/internal_api/sync_manager_impl.cc
+++ b/sync/internal_api/sync_manager_impl.cc
@@ -1359,6 +1359,16 @@ bool SyncManagerImpl::ReceivedExperiment(Experiments* experiments) {
     found_experiment = true;
   }
 
+  ReadNode full_history_sync_node(&trans);
+  if (full_history_sync_node.InitByClientTagLookup(
+          syncer::EXPERIMENTS,
+          syncer::kFullHistorySyncTag) == BaseNode::INIT_OK &&
+      full_history_sync_node.GetExperimentsSpecifics().
+          history_delete_directives().enabled()) {
+    experiments->full_history_sync = true;
+    found_experiment = true;
+  }
+
   return found_experiment;
 }