code: private void checkFinalClassOverrides(Node ctor) {
      if (!isFunctionOrClass(ctor)) {
        return;
      }
  
      JSType type = ctor.getJSType().toMaybeFunctionType();
      if (type != null && type.isConstructor()) {
        JSType finalParentClass = getSuperClassInstanceIfFinal(bestInstanceTypeForMethodOrCtor(ctor));
        if (finalParentClass != null) {
          compiler.report(
              JSError.make(
                  ctor,
                  EXTEND_FINAL_CLASS,
                  type.getDisplayName(),
                  finalParentClass.getDisplayName()));
        }
      }
    }
docs: Checks if a constructor is trying to override a final class.