Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

core/lib/Drupal/Component/Render/MarkupTrait.php

@@ -0,0 +1,82 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Render\MarkupTrait.
+ */
+
+namespace Drupal\Component\Render;
+
+use Drupal\Component\Utility\Unicode;
+
+/**
+ * Implements MarkupInterface and Countable for rendered objects.
+ *
+ * @see \Drupal\Component\Render\MarkupInterface
+ */
+trait MarkupTrait {
+
+  /**
+   * The safe string.
+   *
+   * @var string
+   */
+  protected $string;
+
+  /**
+   * Creates a Markup object if necessary.
+   *
+   * If $string is equal to a blank string then it is not necessary to create a
+   * Markup object. If $string is an object that implements MarkupInterface it
+   * is returned unchanged.
+   *
+   * @param mixed $string
+   *   The string to mark as safe. This value will be cast to a string.
+   *
+   * @return string|\Drupal\Component\Render\MarkupInterface
+   *   A safe string.
+   */
+  public static function create($string) {
+    if ($string instanceof MarkupInterface) {
+      return $string;
+    }
+    $string = (string) $string;
+    if ($string === '') {
+      return '';
+    }
+    $safe_string = new static();
+    $safe_string->string = $string;
+    return $safe_string;
+  }
+
+  /**
+   * Returns the string version of the Markup object.
+   *
+   * @return string
+   *   The safe string content.
+   */
+  public function __toString() {
+    return $this->string;
+  }
+
+  /**
+   * Returns the string length.
+   *
+   * @return int
+   *   The length of the string.
+   */
+  public function count() {
+    return Unicode::strlen($this->string);
+  }
+
+  /**
+   * Returns a representation of the object for use in JSON serialization.
+   *
+   * @return string
+   *   The safe string content.
+   */
+  public function jsonSerialize() {
+    return $this->__toString();
+  }
+
+}