[debugger] Further stepping support in test wrapper

test/mjsunit/debug-step-into-valueof.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 valueOfCallback() {
-  return 2;               // Break 2.
-}                         // Break 3.
-var o = {};
-o.valueOf = valueOfCallback;
-
-Debug.setListener(listener);
-debugger;                 // Break 0.
-var result = 1 + o;       // Break 1.
-Debug.setListener(null);  // Break 4.
-
-assertEquals(3, result);
-assertNull(exception);