Function callback

deps/v8/test/mjsunit/array-reduce.js:1296–1298

(accumulator, currentValue)

  var holey = new Array(10);
  function reduce(a) {
    let callback = function(accumulator, currentValue) {
      return currentValue;
    };
    return a.reduce(callback, 13);
  };
  %PrepareFunctionForOptimization(reduce);