sync: Introduce ModelTypeRegistry and helpers

sync/engine/sync_scheduler_unittest.cc

Index: sync/engine/sync_scheduler_unittest.cc
diff --git a/sync/engine/sync_scheduler_unittest.cc b/sync/engine/sync_scheduler_unittest.cc
index e5876554e81a53bdc4f95d95c8bac398f93bc835..1ec0320a89b9fa79bc424632635ee649f390e3d1 100644
--- a/sync/engine/sync_scheduler_unittest.cc
+++ b/sync/engine/sync_scheduler_unittest.cc
@@ -141,7 +141,7 @@ class SyncSchedulerTest : public testing::Test {
             true,  // enable keystore encryption
             false,  // force enable pre-commit GU avoidance
             "fake_invalidator_client_id"));
-    context_->set_routing_info(routing_info_);
+    context_->SetRoutingInfo(routing_info_);
     context_->set_notifications_enabled(true);
     context_->set_account_name("Test");
     scheduler_.reset(
@@ -890,7 +890,7 @@ TEST_F(SyncSchedulerTest, ConfigurationMode) {
 
   // TODO(tim): Figure out how to remove this dangerous need to reset
   // routing info between mode switches.
-  context()->set_routing_info(routing_info());
+  context()->SetRoutingInfo(routing_info());
   StartSyncScheduler(SyncScheduler::NORMAL_MODE);
 
   RunLoop();