[builtins] move String.prototype[@@iterator] to C++ builtin

BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
@@ skipping 380 matching lines @@
     "src/js/prologue.js",
     "src/js/runtime.js",
     "src/js/v8natives.js",
     "src/js/symbol.js",
     "src/js/array.js",
     "src/js/string.js",
     "src/js/math.js",
     "src/js/regexp.js",
     "src/js/arraybuffer.js",
     "src/js/typedarray.js",
-    "src/js/iterator-prototype.js",
     "src/js/collection.js",
     "src/js/weak-collection.js",
     "src/js/collection-iterator.js",
     "src/js/promise.js",
     "src/js/messages.js",
     "src/js/array-iterator.js",
-    "src/js/string-iterator.js",
     "src/js/templates.js",
     "src/js/spread.js",
     "src/js/proxy.js",
     "src/debug/mirrors.js",
     "src/debug/debug.js",
     "src/debug/liveedit.js",
   ]
 
   outputs = [
     "$target_gen_dir/libraries.cc",
@@ skipping 505 matching lines @@
     "src/builtins/builtins-dataview.cc",
     "src/builtins/builtins-date.cc",
     "src/builtins/builtins-debug.cc",
     "src/builtins/builtins-error.cc",
     "src/builtins/builtins-function.cc",
     "src/builtins/builtins-generator.cc",
     "src/builtins/builtins-global.cc",
     "src/builtins/builtins-handler.cc",
     "src/builtins/builtins-internal.cc",
     "src/builtins/builtins-interpreter.cc",
+    "src/builtins/builtins-iterator.cc",
     "src/builtins/builtins-json.cc",
     "src/builtins/builtins-math.cc",
     "src/builtins/builtins-number.cc",
     "src/builtins/builtins-object.cc",
     "src/builtins/builtins-proxy.cc",
     "src/builtins/builtins-reflect.cc",
     "src/builtins/builtins-sharedarraybuffer.cc",
     "src/builtins/builtins-string.cc",
     "src/builtins/builtins-symbol.cc",
     "src/builtins/builtins-typedarray.cc",
@@ skipping 1826 matching lines @@
     ":fuzzer_support",
     ":lib_wasm_section_fuzzer",
     ":wasm_module_runner",
   ]
 
   configs = [ ":internal_config" ]
 }
 
 v8_fuzzer("wasm_data_section_fuzzer") {
 }