[regexp] Match spec semantics in AdvanceStringIndex

src/regexp/regexp-utils.h

 // Copyright 2016 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.
 
 #ifndef V8_REGEXP_REGEXP_UTILS_H_
 #define V8_REGEXP_REGEXP_UTILS_H_
 
 #include "src/objects.h"
 
 namespace v8 {
@@ skipping 32 matching lines @@
                                         Handle<String> string,
                                         Handle<Object> exec);
 
   // ES#sec-isregexp IsRegExp ( argument )
   // Includes checking of the match property.
   static Maybe<bool> IsRegExp(Isolate* isolate, Handle<Object> object);
 
   // Checks whether exec is identical to the initial RegExp.prototype.exec.
   static bool IsBuiltinExec(Handle<Object> exec);
 
-  // Generic index increment methods respecting unicode surrogate pairs.
+  // ES#sec-advancestringindex
+  // AdvanceStringIndex ( S, index, unicode )
   static int AdvanceStringIndex(Isolate* isolate, Handle<String> string,
                                 int index, bool unicode);
   static MaybeHandle<Object> SetAdvancedStringIndex(Isolate* isolate,
                                                     Handle<JSReceiver> regexp,
                                                     Handle<String> string,
                                                     bool unicode);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_REGEXP_REGEXP_UTILS_H_