initialize static method
Implementation
static Future<void> initialize(FirebaseOptions options, String appId) async {
_appId = appId;
if (_initialized) return;
_initialized = true;
try {
await _initializeInternal(options, appId);
} catch (_) {
// Let a later call retry instead of leaving FCM dead until the next
// app restart (the flag used to stay set after a failure).
_initialized = false;
rethrow;
}
}