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

test/mjsunit/debug-step.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 34 matching lines @@
       result = exec_state.frame().evaluate("i").value();
       // Clear the break point on line 2 if set.
       if (bp2) {
         Debug.clearBreakPoint(bp2);
       }
     }
   }
 };
 
 // Add the debug event listener.
-Debug.addListener(listener);
+Debug.setListener(listener);
 
 // Test debug event for break point.
 function f() {
   for (i = 0; i < 1000; i++) {  //  Line 1.
     x = 1;                      //  Line 2.
   }
 };
 
 // Set a breakpoint on the for statement (line 1).
 bp1 = Debug.setBreakPoint(f, 1);
 
 // Check that performing 1000 steps will make i 499.
 state = 0;
 result = -1;
 f();
 print(state);
 assertEquals(499, result);
 
 // Check that performing 1000 steps with a break point on the statement in the
 // for loop (line 2) will only make i 0 as a real break point breaks even when
 // multiple steps have been requested.
 state = 0;
 result = -1;
 bp2 = Debug.setBreakPoint(f, 2);
 f();
 assertEquals(0, result);
 
 // Get rid of the debug event listener.
-Debug.removeListener(listener);
+Debug.setListener(null);