Simplify debugger state.

test/mjsunit/debug-stepin-positions.js

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 19 matching lines @@
 Debug = debug.Debug
 
 function DebuggerStatement() {
   debugger;  /*pause*/
 }
 
 function TestCase(fun, frame_number) {
   var exception = false;
   var codeSnippet = undefined;
   var resultPositions = undefined;
+  var step = 0;
 
   function listener(event, exec_state, event_data, data) {
     try {
       if (event == Debug.DebugEvent.Break ||
           event == Debug.DebugEvent.Exception) {
-        Debug.setListener(null);
+        if (step++ > 0) return;
         assertHasLineMark(/pause/, exec_state.frame(0));
         assertHasLineMark(/positions/, exec_state.frame(frame_number));
         var frame = exec_state.frame(frame_number);
         codeSnippet = frame.sourceLineText();
         resultPositions = frame.stepInPositions();
       }
     } catch (e) {
       exception = e
     }
 
@@ skipping 158 matching lines @@
 })(Object);
 TestCaseWithDebugger(fun);
 
 // Global function, global object construction, calls before pause point.
 var fun = (function(p) {
   return function() {
     var res = [ Math.abs(new Object()), DebuggerStatement(), Math./*#*/abs(4), /*#*/new Object()./*#*/toString() ]; /*positions*/
   };
 })(Object);
 TestCaseWithDebugger(fun);