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

test/mjsunit/regress/regress-prepare-break-while-recompile.js

 // Copyright 2013 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 36 matching lines @@
 
 foo();
 // Mark and kick off recompilation.
 %OptimizeFunctionOnNextCall(foo, "concurrent");
 foo();
 
 // Set break points on an unrelated function. This clears both optimized
 // and (shared) unoptimized code on foo, and sets both to lazy-compile builtin.
 // Clear the break point immediately after to deactivate the debugger.
 // Do all of this after compile graph has been created.
+Debug.setListener(function(){});
 Debug.setBreakPoint(bar, 0, 0);
 Debug.clearAllBreakPoints();
+Debug.setListener(null);
 
 // At this point, concurrent recompilation is still blocked.
 assertUnoptimized(foo, "no sync");
 // Let concurrent recompilation proceed.
 %UnblockConcurrentRecompilation();
 
 // Install optimized code when concurrent optimization finishes.
 // This needs to be able to deal with shared code being a builtin.
 assertUnoptimized(foo, "sync");