[android][web-browser] Fix WebBrowser sending 'dismiss' before opening

Fixes #6679

TL;DR
A wrong usage of AppState causes WebBrowser to resolve with
`{ type: 'dismiss' }` before opening the view.

This is related to AppState being not initialised yet,
triggering a change before the user leaves the app view
to focus on the browser view.

packages/expo-web-browser/src/WebBrowser.ts

@@ -135,12 +135,22 @@ let _redirectHandler: ((event: RedirectEvent) => void) | null = null;
 // returns to active
 let _onWebBrowserCloseAndroid: null | (() => void) = null;
 
+// Store previous app state to check whether the listener has ever been attached
+let _previousAppState: null | string = AppState.currentState;
+
 function _onAppStateChangeAndroid(state: AppStateStatus) {
+  // if _previousAppState is null, we assume that the first call to
+  // AppState#change event is not actually triggered by a real change
+  // (https://facebook.github.io/react-native/docs/appstate#basic-usage)
+  if (_previousAppState === null) {
+    _previousAppState = state;
+    return;
+  }
+
   if (state === 'active' && _onWebBrowserCloseAndroid) {
     _onWebBrowserCloseAndroid();
   }
 }
-
 async function _openBrowserAndWaitAndroidAsync(startUrl: string): Promise<BrowserResult> {
   let appStateChangedToActive = new Promise(resolve => {
     _onWebBrowserCloseAndroid = resolve;