The Tor Browser / file revision

 // The argument to a breakpoint hit method is a frame.

 var g = newGlobal();

 var dbg = Debugger(g);

 var hits = 0;

 dbg.onDebuggerStatement = function (frame1) {

     function hit(frame2) {

         assertEq(frame2, frame1);

         hits++;

     }

     var s = frame1.script;

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

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

         s.setBreakpoint(offs[i], {hit: hit});

 };

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

        "debugger;\n" +  // line0 + 1

        "x = 1;\n");     // line0 + 2

 assertEq(hits, 1);

 assertEq(g.x, 1);