Fix memory_scratch_sink_test in debug mode (#1906)

be/src/runtime/runtime_state.cpp

@@ -264,6 +264,11 @@ Status RuntimeState::init_mem_trackers(const TUniqueId& query_id) {
     return Status::OK();
 }
 
+Status RuntimeState::init_instance_mem_tracker() {
+    _instance_mem_tracker.reset(new MemTracker(-1));
+    return Status::OK();
+}
+
 Status RuntimeState::init_buffer_poolstate() {
   ExecEnv* exec_env = ExecEnv::GetInstance();
   int64_t mem_limit = _query_mem_tracker->lowest_limit();

be/src/runtime/runtime_state.h

@@ -93,6 +93,9 @@ public:
     // This function also initializes a user function mem tracker (in the fourth level).
     Status init_mem_trackers(const TUniqueId& query_id);
 
+    // for ut only
+    Status init_instance_mem_tracker();
+
     /// Called from Init() to set up buffer reservations and the file group.
     Status init_buffer_poolstate();