websocket connection - make it work with new js sdk

Summary:
we used to send plugins list with connect command, now we can respond to getPlugins request with new api.
we still support old clients

Reviewed By: jknoxville

Differential Revision: D23625139

fbshipit-source-id: 37a24d0c83cd879d93287dd3a3d4d5d2f9477b34

desktop/app/src/utils/js-client-server-utils/websocketClientFlipperConnection.tsx

@@ -18,7 +18,7 @@ export class WebsocketClientFlipperConnection<M>
   connStatusSubscribers: Set<ISubscriber<ConnectionStatus>> = new Set();
   connStatus: ConnectionStatus;
   app: string;
-  plugins: string[] = [];
+  plugins: string[] | undefined = undefined;
 
   constructor(ws: WebSocket, app: string, plugins: string[]) {
     this.websocket = ws;
@@ -66,7 +66,7 @@ export class WebsocketClientFlipperConnection<M>
 
       subscriber.onSubscribe(() => {});
 
-      if (method === 'getPlugins') {
+      if (method === 'getPlugins' && this.plugins != null) {
         subscriber.onComplete({
           data: JSON.stringify({
             success: {plugins: this.plugins},