[debugger] flood function for stepping before calling it.

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;
-var exception = null;
 
 function listener(event, exec_state, event_data, data) {
   if (event != Debug.DebugEvent.Break) return;
   try {
-    var source_line = exec_state.frame(0).sourceLineText();
-    print(source_line);
+    print(event_data.sourceLineText());
+    assertTrue(event_data.sourceLineText().indexOf(`Break ${break_count++}.`) > 0);
     exec_state.prepareStep(Debug.StepAction.StepIn, 1);
-    break_count++;
   } catch (e) {
     exception = e;
   }
-}
+};
 
-var Debug = debug.Debug;
+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.
 
-
-function f() {
-  this.x = 1;
-}
-
-function g() {
-  new f();
-}
-
-Debug.setBreakPoint(g, 6, Debug.BreakPositionAlignment.BreakPosition);
-print(Debug.showBreakPoints(g, undefined,
-      Debug.BreakPositionAlignment.BreakPosition));
-
-g();
-Debug.setListener(null);
-
-assertEquals(6, break_count);
+assertEquals(3, result);
 assertNull(exception);