fix(crashlytics): ensure main thread execution for test event success callback

Author: SelaseKay

packages/firebase_crashlytics/firebase_crashlytics/android/src/main/java/io/flutter/plugins/firebase/crashlytics/FlutterFirebaseCrashlyticsPlugin.java

@@ -150,6 +150,7 @@ private Task<Map<String, Object>> didCrashOnPreviousExecution() {
 
   private Task<Void> recordError(final Map<String, Object> arguments) {
     TaskCompletionSource<Void> taskCompletionSource = new TaskCompletionSource<>();
+    Handler mainHandler = new Handler(Looper.getMainLooper());
 
     cachedThreadPool.execute(
         () -> {
@@ -178,7 +179,7 @@ private Task<Void> recordError(final Map<String, Object> arguments) {
             if (reason != null) {
               final String crashlyticsErrorReason = "thrown" + reason;
               if (isRunningInCI() && testEventSink != null) {
-                testEventSink.success(crashlyticsErrorReason);
+                mainHandler.post(() -> testEventSink.success(crashlyticsErrorReason));
               }
               // Set a "reason" (to match iOS) to show where the exception was thrown.
               crashlytics.setCustomKey(Constants.FLUTTER_ERROR_REASON, crashlyticsErrorReason);

tests/integration_test/firebase_crashlytics/firebase_crashlytics_e2e_test.dart

@@ -117,6 +117,8 @@ void main() {
             reason: 'foo reason',
           );
 
+          await Future.delayed(const Duration(seconds: 3));
+
           expect(capturedEvents, ['thrown foooo reason']);
 
           },