Set properties via constructor.

Closes #3427737

core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/AllowedValuesConstraint.php

@@ -17,8 +17,14 @@
 )]
 class AllowedValuesConstraint extends Choice {
 
-  public $strict = TRUE;
-  public $minMessage = 'You must select at least %limit choice.|You must select at least %limit choices.';
-  public $maxMessage = 'You must select at most %limit choice.|You must select at most %limit choices.';
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(...$args) {
+    $this->strict = TRUE;
+    $this->minMessage = 'You must select at least %limit choice.|You must select at least %limit choices.';
+    $this->maxMessage = 'You must select at most %limit choice.|You must select at most %limit choices.';
+    parent::__construct(...$args);
+  }
 
 }