Fix trivial type-check errors in file_manager.

ui/file_manager/file_manager/background/js/device_handler.js

Index: ui/file_manager/file_manager/background/js/device_handler.js
diff --git a/ui/file_manager/file_manager/background/js/device_handler.js b/ui/file_manager/file_manager/background/js/device_handler.js
index bf79b40c4fb6918d3a92c5b10f0c1c496c7af246..ede54098f505c1ab065868d0e40aedc21991e81a 100644
--- a/ui/file_manager/file_manager/background/js/device_handler.js
+++ b/ui/file_manager/file_manager/background/js/device_handler.js
@@ -192,7 +192,7 @@ DeviceHandler.Notification.prototype.showOnce = function(devicePath) {
 
 /**
  * Shows the notificaiton without using AsyncQueue.
- * @param {string} notificaitonId Notification ID.
+ * @param {string} notificationId Notification ID.
  * @param {?string} message Message overriding the normal message.
  * @param {function()} callback Callback to be invoked when the notification is
  *     created.
@@ -302,14 +302,13 @@ DeviceHandler.prototype.onMountCompleted_ = function(event) {
   // If this is remounting, which happens when resuming ChromeOS, the device has
   // already inserted to the computer. So we suppress the notification.
   var volume = event.volumeMetadata;
-  if (!volume.deviceType || !event.shouldNotify)
+  if (!volume.deviceType || !volume.devicePath || !event.shouldNotify)
     return;
 
   // If the current volume status is succeed and it should be handled in
   // Files.app, show the notification to navigate the volume.
   if (event.eventType === 'mount' && event.status === 'success') {
-    DeviceHandler.Notification.DEVICE_NAVIGATION.show(
-        event.volumeMetadata.devicePath);
+    DeviceHandler.Notification.DEVICE_NAVIGATION.show(volume.devicePath);
   } else if (event.eventType === 'unmount') {
     DeviceHandler.Notification.DEVICE_NAVIGATION.hide(volume.devicePath);
   }