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

vendor/psr/log/Psr/Log/LoggerAwareTrait.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Psr\Log;
+
+/**
+ * Basic Implementation of LoggerAwareInterface.
+ */
+trait LoggerAwareTrait
+{
+    /** @var LoggerInterface */
+    protected $logger;
+
+    /**
+     * Sets a logger.
+     * 
+     * @param LoggerInterface $logger
+     */
+    public function setLogger(LoggerInterface $logger)
+    {
+        $this->logger = $logger;
+    }
+}