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

test/mjsunit/regress/regress-1081309.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 72 matching lines @@
     assertEquals("", response.lookup(backtrace.frames[1].func.ref).name);
 
     listenerCalled = true;
   }
   } catch (e) {
     exception = e
   };
 };
 
 // Add the debug event listener.
-Debug.addListener(listener);
+Debug.setListener(listener);
 
 // Call method on undefined.
 function g() {
   (void 0).f();
 };
 
 // Break on the exception to do a backtrace with undefined as receiver.
 Debug.setBreakOnException(true);
 try {
   g();
 } catch(e) {
   // Ignore the exception "Cannot call method 'x' of undefined"
 }
 
 // Make sure that the debug event listener vas invoked.
 assertTrue(listenerCalled, "listener not called");
 assertFalse(exception, "exception in listener", exception)