Implement sending messages from desktop to add-on

Reviewed By: antonk52

Differential Revision: D34239803

fbshipit-source-id: 1a18d522ba877ade3d0703fbb374c15b596241d7

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

@@ -69,7 +69,7 @@ export class SandyDevicePluginInstance extends BasePluginInstance {
   }
 
   /** client that is bound to this instance */
-  readonly client: DevicePluginClient;
+  readonly client: DevicePluginClient<any, any>;
 
   constructor(
     serverAddOnControls: ServerAddOnControls,

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

@@ -379,9 +379,13 @@ export abstract class BasePluginInstance {
         this.flipperLib.showNotification(this.pluginKey, notification);
       },
       logger: this.flipperLib.logger,
-      sendToServerAddOn: (_method, _params): any => {
-        // TODO: Implement me
-      },
+      sendToServerAddOn: (method, params) =>
+        this.serverAddOnControls.sendMessage(
+          this.definition.packageName,
+          // TODO: Remove type cast
+          method as string,
+          params,
+        ),
       onServerAddOnMessage: (_event, _cb) => {
         // TODO: Implement me
       },