Files.app: fix some closure compilation issues to unblock new compiler roll.

ui/file_manager/file_manager/foreground/js/file_manager.js

Index: ui/file_manager/file_manager/foreground/js/file_manager.js
diff --git a/ui/file_manager/file_manager/foreground/js/file_manager.js b/ui/file_manager/file_manager/foreground/js/file_manager.js
index b3cbf399810cb7e22c0d4c60d1455e3d028f4451..ff55f9622f1e2bf1fcaccc30cf7a41177cb8dae6 100644
--- a/ui/file_manager/file_manager/foreground/js/file_manager.js
+++ b/ui/file_manager/file_manager/foreground/js/file_manager.js
@@ -439,7 +439,7 @@ FileManager.prototype = /** @struct */ {
                 /** @type {!importer.ImportRunner} */ (
                     this.mediaImportHandler_),
                 new importer.RuntimeCommandWidget(),
-                this.tracker_);
+                assert(this.tracker_));
           }
         }.bind(this));