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

src/runtime/runtime-array.cc

 // Copyright 2014 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.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/conversions-inl.h"
 #include "src/elements.h"
 #include "src/factory.h"
@@ skipping 471 matching lines @@
 
 
 RUNTIME_FUNCTION(Runtime_GetCachedArrayIndex) {
   // This can never be reached, because Runtime_HasCachedArrayIndex always
   // returns false.
   UNIMPLEMENTED();
   return nullptr;
 }
 
 
+RUNTIME_FUNCTION(Runtime_FastOneByteArrayJoin) {
+  SealHandleScope shs(isolate);
+  DCHECK(args.length() == 2);
+  // Returning undefined means that this fast path fails and one has to resort
+  // to a slow path.
+  return isolate->heap()->undefined_value();
+}
+
+
 RUNTIME_FUNCTION(Runtime_ArraySpeciesConstructor) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(Object, original_array, 0);
   Handle<Object> constructor;
   ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
       isolate, constructor,
       Object::ArraySpeciesConstructor(isolate, original_array));
   return *constructor;
 }
 
 }  // namespace internal
 }  // namespace v8