Revert of [fullcodegen] Remove the hacky %_FastOneByteArrayJoin intrinsic.

src/js/array.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function(global, utils, extrasUtils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 191 matching lines @@
 
     // We pull the empty separator check outside the loop for speed!
     if (separator.length == 0) {
       var elements_length = 0;
       for (var i = 0; i < length; i++) {
         var e = array[i];
         if (!IS_STRING(e)) e = convert(e);
         elements[elements_length++] = e;
       }
       elements.length = elements_length;
+      var result = %_FastOneByteArrayJoin(elements, '');
+      if (!IS_UNDEFINED(result)) return result;
       return %StringBuilderConcat(elements, elements_length, '');
     }
     // Non-empty separator case.
     // If the first element is a number then use the heuristic that the
     // remaining elements are also likely to be numbers.
     if (!IS_NUMBER(array[0])) {
       for (var i = 0; i < length; i++) {
         var e = array[i];
         if (!IS_STRING(e)) e = convert(e);
         elements[i] = e;
       }
     } else {
       for (var i = 0; i < length; i++) {
         var e = array[i];
         if (IS_NUMBER(e)) {
           e = %_NumberToString(e);
         } else if (!IS_STRING(e)) {
           e = convert(e);
         }
         elements[i] = e;
       }
     }
+    var result = %_FastOneByteArrayJoin(elements, separator);
+    if (!IS_UNDEFINED(result)) return result;
+
     return %StringBuilderJoin(elements, length, separator);
   } finally {
     // Make sure to remove the last element of the visited array no
     // matter what happens.
     if (is_array) visited_arrays.length = visited_arrays.length - 1;
   }
 }
 
 
 function ConvertToString(x) {
@@ skipping 191 matching lines @@
 }
 
 
 function InnerArrayJoin(separator, array, length) {
   if (IS_UNDEFINED(separator)) {
     separator = ',';
   } else {
     separator = TO_STRING(separator);
   }
 
+  var result = %_FastOneByteArrayJoin(array, separator);
+  if (!IS_UNDEFINED(result)) return result;
+
   // Fast case for one-element arrays.
   if (length === 1) {
     var e = array[0];
     if (IS_NULL_OR_UNDEFINED(e)) return '';
     return TO_STRING(e);
   }
 
   return Join(array, length, separator, ConvertToString);
 }
 
@@ skipping 1496 matching lines @@
 %InstallToContext([
   "array_pop", ArrayPop,
   "array_push", ArrayPush,
   "array_shift", ArrayShift,
   "array_splice", ArraySplice,
   "array_slice", ArraySlice,
   "array_unshift", ArrayUnshift,
 ]);
 
 });