The Tor Browser / file revision

 function A(a) { this.a = a; }

 A.prototype.foo = function (x) {};

 function B(b) { this.b = b; }

 B.prototype.foo = function (x) {};

 function C(c) {}

 function makeArray(n) {

     var classes = [A, B, C];

     var arr = [];

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

         arr.push(new classes[i % 3](i % 3));

     }

     return arr;

 }

 function runner(arr, resultArray, len) {

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

         var obj = arr[i];

         resultArray[0] += obj.foo(i);

     }

 }

 var resultArray = [0];

 var arr = makeArray(30000);

 C.prototype.foo = Uint8ClampedArray;

 runner(arr, resultArray, 30000);