Issue #2646786 by dawehner: Add a backtrace for logged exceptions

core/lib/Drupal/Core/Utility/Error.php

@@ -76,6 +76,7 @@ public static function decodeException($exception) {
       '%line' => $caller['line'],
       'severity_level' => static::ERROR,
       'backtrace' => $backtrace,
+      'backtrace_string' => $exception->getTraceAsString(),
     );
   }