[regexp] Match spec semantics in AdvanceStringIndex

src/regexp/regexp-utils.h

Index: src/regexp/regexp-utils.h
diff --git a/src/regexp/regexp-utils.h b/src/regexp/regexp-utils.h
index e57bd11f60d2758a8805159eadcee1d3285934dc..217f0c14d6730bcad715f1b356fc92ef6402fad1 100644
--- a/src/regexp/regexp-utils.h
+++ b/src/regexp/regexp-utils.h
@@ -50,7 +50,8 @@ class RegExpUtils : public AllStatic {
   // 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,