Debugger: require debugger to be active when dealing with breaks.

test/mjsunit/regress/regress-2318.js

 // Copyright 2012 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 38 matching lines @@
   var _P0 = 75; var _P1 = 76; var _P2 = 77; var _P3 = 78; var _P4 = 79;
   var _Q0 = 80; var _Q1 = 81; var _Q2 = 82; var _Q3 = 83; var _Q4 = 84;
   var _R0 = 85; var _R1 = 86; var _R2 = 87; var _R3 = 88; var _R4 = 89;
   var _S0 = 90; var _S1 = 91; var _S2 = 92; var _S3 = 93; var _S4 = 94;
   var _T0 = 95; var _T1 = 96; var _T2 = 97; var _T3 = 98; var _T4 = 99;
 
   f();
 };
 
 Debug = debug.Debug;
-var bp = Debug.setBreakPoint(f, 0);
 
 function listener(event, exec_state, event_data, data) {
   result = exec_state.frame().evaluate("i").value();
 };
 
 Debug.setListener(listener);
+var bp = Debug.setBreakPoint(f, 0);
+
 assertThrows(function() { f(); }, RangeError);