add stack method

src/Illuminate/Log/LogManager.php

@@ -65,6 +65,21 @@ public function __construct($app)
         $this->app = $app;
     }
 
+    /**
+     * Create a new, on-demand aggregate logger instance.
+     *
+     * @param  array  $channels
+     * @param  string|null  $channel
+     * @return \Psr\Log\LoggerInterface
+     */
+    public function stack(array $channels, $channel = null)
+    {
+        return new Logger(
+            $this->createAggregateDriver(compact('channels', 'channel')),
+            $this->app['events']
+        );
+    }
+
     /**
      * Get a log channel instance.
      *