[debugger] Further stepping support in test wrapper

test/debugger/debug/debug-stack-check-position.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --expose-debug-as debug --allow-natives-syntax
 
 var Debug = debug.Debug;
 var exception = null;
 var loop = true;
 
 function listener(event, exec_state, event_data, data) {
   if (event != Debug.DebugEvent.Break) return;
   try {
     assertTrue(exec_state.frame(0).sourceLineText().indexOf("BREAK") > 0);
   } catch (e) {
     exception = e;
   }
 }
 
 function f() {     // BREAK
   return 1;
 }
 
 Debug.setListener(listener);
 
 %ScheduleBreak();  // Break on function entry.
 f();
 
 Debug.setListener(null);
 assertNull(exception);