Only count legacy parser usage if legacy parser had effect.

src/dateparser-inl.h

Index: src/dateparser-inl.h
diff --git a/src/dateparser-inl.h b/src/dateparser-inl.h
index 57e4fa5e6789dd2ee9540d42ea808c6e0e4d1ea9..47a7c6e7ff1e8c8f1b574ad8478574ad80be3d49 100644
--- a/src/dateparser-inl.h
+++ b/src/dateparser-inl.h
@@ -75,11 +75,12 @@ bool DateParser::Parse(Isolate* isolate, Vector<Char> str, FixedArray* out) {
   if (next_unhandled_token.IsInvalid()) return false;
   bool has_read_number = !day.IsEmpty();
   // If there's anything left, continue with the legacy parser.
-  bool legacy_parser = !next_unhandled_token.IsEndOfInput();
+  bool legacy_parser = false;
   for (DateToken token = next_unhandled_token;
        !token.IsEndOfInput();
        token = scanner.Next()) {
     if (token.IsNumber()) {
+      legacy_parser = true;
       has_read_number = true;
       int n = token.number();
       if (scanner.SkipSymbol(':')) {
@@ -115,6 +116,7 @@ bool DateParser::Parse(Isolate* isolate, Vector<Char> str, FixedArray* out) {
         scanner.SkipSymbol('-');
       }
     } else if (token.IsKeyword()) {
+      legacy_parser = true;
       // Parse a "word" (sequence of chars. >= 'A').
       KeywordType type = token.keyword_type();
       int value = token.keyword_value();
@@ -133,6 +135,7 @@ bool DateParser::Parse(Isolate* isolate, Vector<Char> str, FixedArray* out) {
         if (scanner.Peek().IsNumber()) return false;
       }
     } else if (token.IsAsciiSign() && (tz.IsUTC() || !time.IsEmpty())) {
+      legacy_parser = true;
       // Parse UTC offset (only after UTC or time).
       tz.SetSign(token.ascii_sign());
       // The following number may be empty.