sync: Introduce ModelTypeRegistry and helpers

sync/engine/syncer_unittest.cc

Index: sync/engine/syncer_unittest.cc
diff --git a/sync/engine/syncer_unittest.cc b/sync/engine/syncer_unittest.cc
index 19aff7c3b115dd63a34d50cfb9bb53e03360d0f5..6136c070406721d9067e3e1f319898fc11ff26f6 100644
--- a/sync/engine/syncer_unittest.cc
+++ b/sync/engine/syncer_unittest.cc
@@ -233,7 +233,7 @@ class SyncerTest : public testing::Test,
             true,  // enable keystore encryption
             false,  // force enable pre-commit GU avoidance experiment
             "fake_invalidator_client_id"));
-    context_->set_routing_info(routing_info);
+    context_->SetRoutingInfo(routing_info);
     syncer_ = new Syncer(&cancelation_signal_);
 
     syncable::ReadTransaction trans(FROM_HERE, directory());
@@ -442,7 +442,7 @@ class SyncerTest : public testing::Test,
     GetModelSafeRoutingInfo(&routing_info);
 
     if (context_) {
-      context_->set_routing_info(routing_info);
+      context_->SetRoutingInfo(routing_info);
     }
 
     mock_server_->ExpectGetUpdatesRequestTypes(enabled_datatypes_);
@@ -455,7 +455,7 @@ class SyncerTest : public testing::Test,
     GetModelSafeRoutingInfo(&routing_info);
 
     if (context_) {
-      context_->set_routing_info(routing_info);
+      context_->SetRoutingInfo(routing_info);
     }
 
     mock_server_->ExpectGetUpdatesRequestTypes(enabled_datatypes_);