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

src/objects-debug.cc

 // 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.
 
 #include "src/objects.h"
 
 #include "src/bootstrapper.h"
 #include "src/disasm.h"
 #include "src/disassembler.h"
 #include "src/field-type.h"
@@ skipping 134 matching lines @@
       break;
     case JS_MAP_TYPE:
       JSMap::cast(this)->JSMapVerify();
       break;
     case JS_SET_ITERATOR_TYPE:
       JSSetIterator::cast(this)->JSSetIteratorVerify();
       break;
     case JS_MAP_ITERATOR_TYPE:
       JSMapIterator::cast(this)->JSMapIteratorVerify();
       break;
+    case JS_STRING_ITERATOR_TYPE:
+      JSStringIterator::cast(this)->JSStringIteratorVerify();
+      break;
     case JS_WEAK_MAP_TYPE:
       JSWeakMap::cast(this)->JSWeakMapVerify();
       break;
     case JS_WEAK_SET_TYPE:
       JSWeakSet::cast(this)->JSWeakSetVerify();
       break;
     case JS_REGEXP_TYPE:
       JSRegExp::cast(this)->JSRegExpVerify();
       break;
     case FILLER_TYPE:
@@ skipping 607 matching lines @@
 }
 
 
 void JSWeakMap::JSWeakMapVerify() {
   CHECK(IsJSWeakMap());
   JSObjectVerify();
   VerifyHeapPointer(table());
   CHECK(table()->IsHashTable() || table()->IsUndefined(GetIsolate()));
 }
 
+void JSStringIterator::JSStringIteratorVerify() {
+  CHECK(IsJSStringIterator());
+  JSObjectVerify();
+  CHECK(string()->IsString());
+  CHECK_GE(index(), 0);
+  CHECK_LE(index(), String::kMaxLength);
+}
 
 void JSWeakSet::JSWeakSetVerify() {
   CHECK(IsJSWeakSet());
   JSObjectVerify();
   VerifyHeapPointer(table());
   CHECK(table()->IsHashTable() || table()->IsUndefined(GetIsolate()));
 }
 
 
 void JSRegExp::JSRegExpVerify() {
@@ skipping 559 matching lines @@
 
   // Both are done at the same time.
   CHECK_EQ(new_it.done(), old_it.done());
 }
 
 
 #endif  // DEBUG
 
 }  // namespace internal
 }  // namespace v8