cleanup: Mark globals used from other modules as exported

eslint cannot figure out that those symbols are used from other modules
via imports, so they trigger unused-variable errors. To fix, explicitly
mark those symbols as exported.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/627

js/perf/core.js

@@ -1,4 +1,8 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
+/* exported run, script_overviewShowStart, script_overviewShowDone,
+            script_applicationsShowStart, script_applicationsShowDone,
+            script_afterShowHide, malloc_usedSize, glx_swapComplete,
+            clutter_stagePaintDone */
 
 const System = imports.system;