Expose GK api on client

Summary: Make sure that GKs can be used in pure sandy plugins.

Reviewed By: jknoxville

Differential Revision: D25368358

fbshipit-source-id: c7c6aa4ecf0443cb3b5d90e22e8aca9a73a69389

desktop/flipper-plugin/src/plugin/FlipperLib.tsx

@@ -15,4 +15,5 @@ import {NormalizedMenuEntry} from './MenuEntry';
 export interface FlipperLib {
   enableMenuEntries(menuEntries: NormalizedMenuEntry[]): void;
   createPaste(input: string): Promise<string | undefined>;
+  GK(gatekeeper: string): boolean;
 }