Fixed bug where message could get lost if plugin was selected

Summary:
If the analytics plugin was in the foreground, and messages arrived in quick succession, some messages would not be processed.

Although the code was tested, there were not enough assertions to make sure the loop was correct. coverage !== correctness {emoji:1f605}

This fixes T68101450

Changelog: Fixed regression where analytics messages where lost

Reviewed By: jknoxville

Differential Revision: D21929679

fbshipit-source-id: c9fe2b18a249e40085d99914a809abf14fa7cf8f

desktop/app/src/utils/__tests__/messageQueue.node.tsx

@@ -88,13 +88,18 @@ function selectTestPlugin(store: Store, client: Client) {
 test('queue - events are processed immediately if plugin is selected', async () => {
   await createMockFlipperWithPlugin(
     TestPlugin,
-    async ({store, sendMessage}) => {
+    async ({store, client, sendMessage}) => {
       expect(store.getState().connections.selectedPlugin).toBe('TestPlugin');
+      sendMessage('noop', {});
+      sendMessage('noop', {});
       sendMessage('inc', {});
+      sendMessage('inc', {delta: 4});
+      sendMessage('noop', {});
+      client.flushMessageBuffer();
       expect(store.getState().pluginStates).toMatchInlineSnapshot(`
           Object {
             "TestApp#Android#MockAndroidDevice#serial#TestPlugin": Object {
-              "count": 1,
+              "count": 5,
             },
           }
         `);

desktop/app/src/utils/messageQueue.tsx

@@ -172,10 +172,10 @@ export function processMessagesImmediately(
   messages: Message[],
 ) {
   const persistedState = getCurrentPluginState(store, plugin, pluginKey);
-  let newPluginState: any;
-  messages.forEach((message) => {
-    newPluginState = processMessage(persistedState, pluginKey, plugin, message);
-  });
+  const newPluginState = messages.reduce(
+    (state, message) => processMessage(state, pluginKey, plugin, message),
+    persistedState,
+  );
   if (persistedState !== newPluginState) {
     store.dispatch(
       setPluginState({