[Sync] Add ModelTypeStore implementation.

sync/api/model_type_store.cc

Index: sync/api/model_type_store.cc
diff --git a/sync/api/model_type_store.cc b/sync/api/model_type_store.cc
index 657932dcaecb49d1c51231b727b66897279559eb..72af046757ac0228ecede563fe30c134baa4a630 100644
--- a/sync/api/model_type_store.cc
+++ b/sync/api/model_type_store.cc
@@ -4,13 +4,13 @@
 
 #include "sync/api/model_type_store.h"
 
-#include "base/logging.h"
+#include "sync/internal_api/public/model_type_store_impl.h"
 
 namespace syncer_v2 {
 
 // static
 void ModelTypeStore::CreateInMemoryStoreForTest(const InitCallback& callback) {
-  NOTIMPLEMENTED();
+  ModelTypeStoreImpl::CreateInMemoryStoreForTest(callback);
 }
 
 ModelTypeStore::~ModelTypeStore() {}