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

test/mjsunit/es6/debug-evaluate-blockscopes.js

 // Copyright 2011 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 30 matching lines @@
     try {             // Line 3.
       throw 'stuff';  // Line 4.
     } catch (e) {     // Line 5.
       x = 2;          // Line 6.
     }
   }
 };
 
 // Get the Debug object exposed from the debug context global object.
 var Debug = debug.Debug
-// Set breakpoint on line 6.
-var bp = Debug.setBreakPoint(f, 6);
 
 function listener(event, exec_state, event_data, data) {
   if (event == Debug.DebugEvent.Break) {
     result = exec_state.frame().evaluate("i").value();
   }
 };
 
 // Add the debug event listener.
 Debug.setListener(listener);
+
+//Set breakpoint on line 6.
+var bp = Debug.setBreakPoint(f, 6);
+
 result = -1;
 f();
 assertEquals(1, result);
 
 // Clear breakpoint.
 Debug.clearBreakPoint(bp);
 // Get rid of the debug event listener.
 Debug.setListener(null);
 
 
@@ skipping 28 matching lines @@
     exception = e;
   }
 });
 
 exception = null;
 f1();
 assertEquals(null, exception, exception);
 exception = null;
 f2();
 assertEquals(null, exception, exception);
+
+Debug.setListener(null);