Skip unexpected events in MultiPlatformViewBackgroundForegroundScenar…

…io (flutter#48456)

Fixes flutter/flutter#138193.

Was first attempted to fix in flutter#48096, but that was not reliable since it's all asynchronous. 

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

testing/scenario_app/lib/src/platform_view.dart

@@ -510,6 +510,13 @@ class MultiPlatformViewBackgroundForegroundScenario extends Scenario
     PlatformMessageResponseCallback? callback,
   ) {
     final String message = utf8.decode(data!.buffer.asUint8List());
+
+    // The expected first event should be 'AppLifecycleState.resumed', but
+    // occasionally it will receive 'AppLifecycleState.inactive' first. Skip
+    // any messages until 'AppLifecycleState.resumed' is received.
+    if (_lastLifecycleState.isEmpty && message != 'AppLifecycleState.resumed') {
+      return;
+    }
     if (_lastLifecycleState == 'AppLifecycleState.inactive' &&
         message == 'AppLifecycleState.resumed') {
       _nextFrame = _secondFrame;