The Tor Browser / file revision

 // A single Debugger object can set multiple breakpoints at an instruction.

 var g = newGlobal();

 var dbg = Debugger(g);

 var log = '';

 dbg.onDebuggerStatement = function (frame) {

     log += 'D';

     function handler(i) {

         return {hit: function (frame) { log += '' + i; }};

     }

     var f = frame.eval("f").return;

     var s = f.script;

     var offs = s.getLineOffsets(g.line0 + 2);

     for (var i = 0; i < 10; i++) {

         var bp = handler(i);

         for (var j = 0; j < offs.length; j++)

             s.setBreakpoint(offs[j], bp);

     }

     assertEq(f.call().return, 42);

     log += 'X';

 };

 g.eval("var line0 = Error().lineNumber;\n" +

        "function f() {\n" +  // line0 + 1

        "    return 42;\n" +  // line0 + 2

        "}\n" +

        "debugger;\n");

 assertEq(log, 'D0123456789X');