[debugger] Further stepping support in test wrapper

test/mjsunit/debug-step-end-of-script.js

-// Copyright 2015 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 expected = ["debugger;", "debugger;"];
-
-function listener(event, exec_state, event_data, data) {
-  if (event != Debug.DebugEvent.Break) return;
-  try {
-    assertEquals(expected.shift(), exec_state.frame(0).sourceLineText());
-    exec_state.prepareStep(Debug.StepAction.StepNext);
-  } catch (e) {
-    %AbortJS(e + "\n" + e.stack);
-  }
-}
-
-Debug.setListener(listener);
-debugger;