Pass supportsMethod as an argument to the exportPersistedState

Summary:
This diff adds supportsMethod as a closure which can be used to verify a method is implemented on the client side.

It will be used in the next diff

Reviewed By: jknoxville

Differential Revision: D21176415

fbshipit-source-id: fe16d966c58d36558034ce4ade8f58f8031aab18

desktop/app/src/plugin.tsx

@@ -31,6 +31,15 @@ export function callClient(
   return (method, params) => client.call(id, method, false, params);
 }
 
+// This function is intended to be called from outside of the plugin.
+// If you want to `supportsMethod` from the plugin use, this.client.supportsMethod
+export function supportsMethod(
+  client: Client,
+  id: string,
+): (method: string) => Promise<boolean> {
+  return (method) => client.supportsMethod(id, method);
+}
+
 export interface PluginClient {
   // eslint-disable-next-line
   send(method: string, params?: Parameters): void;
@@ -109,6 +118,7 @@ export abstract class FlipperBasePlugin<
         store: ReduxState | undefined,
         idler?: Idler,
         statusUpdate?: (msg: string) => void,
+        supportsMethod?: (method: string) => Promise<boolean>,
       ) => Promise<StaticPersistedState | undefined>)
     | null;
   static getActiveNotifications: