[debugger] Further stepping support in test wrapper

test/mjsunit/debug-stepin-builtin-callback-opt.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
-
-Debug = debug.Debug
-
-var exception = null;
-var break_count = 0;
-
-function listener(event, exec_state, event_data, data) {
-  if (event != Debug.DebugEvent.Break) return;
-  try {
-    print(event_data.sourceLineText());
-    assertTrue(
-        event_data.sourceLineText().indexOf(`Break ${break_count++}.`) > 0);
-    exec_state.prepareStep(Debug.StepAction.StepIn);
-  } catch (e) {
-    exception = e;
-  }
-};
-
-function replaceCallback(a) {
-  return "x";                                   // Break 2.
-}                                               // Break 3.
-
-var re = /x/g;
-// Optimize the inner helper function for string replace.
-for (var i = 0; i < 10000; i++) "x".replace(re, replaceCallback);
-
-Debug.setListener(listener);
-debugger;                                       // Break 0.
-var result = "x".replace(re, replaceCallback);  // Break 1.
-Debug.setListener(null);                        // Break 4.
-
-assertNull(exception);