Changed the debugger API to allow only one debug event listener to be registe...

test/mjsunit/debug-step-stub-callfunction.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 24 matching lines @@
   if (event == Debug.DebugEvent.Break) {
     break_break_point_hit_count++;
     // Continue stepping until returned to bottom frame.
     if (exec_state.frameCount() > 1) {
       exec_state.prepareStep(Debug.StepAction.StepIn);
     }
   }
 };
 
 // Add the debug event listener.
-Debug.addListener(listener);
+Debug.setListener(listener);
 
 // Use 'eval' to ensure that the call to print is through CodeStub CallFunction.
 // See Ia32CodeGenerator::VisitCall and Ia32CodeGenerator::CallWithArguments.
 function f() {
   debugger;
   eval('');
   print('Hello, world!');
 };
 
 break_break_point_hit_count = 0;
 f();
 assertEquals(5, break_break_point_hit_count);
 
 // Use an inner function to ensure that the function call is through CodeStub
 // CallFunction see Ia32CodeGenerator::VisitCall and
 // Ia32CodeGenerator::CallWithArguments.
 function g() {
   function h() {}
   debugger;
   h();
 };
 
 break_break_point_hit_count = 0;
 g();
 assertEquals(4, break_break_point_hit_count);
 
 // Get rid of the debug event listener.
-Debug.removeListener(listener);
+Debug.setListener(null);