[parser] Allow duplicate __proto__ keys in patterns

src/parsing/expression-classifier.h

Index: src/parsing/expression-classifier.h
diff --git a/src/parsing/expression-classifier.h b/src/parsing/expression-classifier.h
index 8e13d0e503756a4c841919348590e7abb302e31d..c4a6a214258b2800e8a8d04e3777061169b40320 100644
--- a/src/parsing/expression-classifier.h
+++ b/src/parsing/expression-classifier.h
@@ -345,6 +345,13 @@ class ExpressionClassifier {
     invalid_productions_ &= ~AssignmentPatternProduction;
   }
 
+  void ForgiveExpressionError() {
+    if (!(invalid_productions_ & ExpressionProduction)) return;
+    Error& e = reported_error(kExpressionProduction);
+    e.kind = kUnusedError;
+    invalid_productions_ &= ~ExpressionProduction;
+  }
+
   void Accumulate(ExpressionClassifier* inner,
                   unsigned productions = StandardProductions,
                   bool merge_non_patterns = true) {