Add onMessage getter to WindowEventGetters extension methods (#95)

* Add `onMessage` getter to `WindowEventGetters` extension methods

* Export `providers.dart` from `helpers.dart`

* changelog

* Update CHANGELOG.md

Co-authored-by: Kevin Moore <kevmoo@users.noreply.github.com>

---------

Co-authored-by: Kevin Moore <kevmoo@users.noreply.github.com>

Author: kenzieschmoll

CHANGELOG.md

@@ -1,4 +1,6 @@
 ## 0.3.1-dev
+- Add `onMessage` getter to `WindowEventGetters` extension methods.
+- `helpers.dart`: expose the `EventStreamProviders` class.
 - Add `createIFrameElement` method to `helpers.dart`.
 - Updated types to account for union types.
 - Fixed issue where all `JSAny`s were treated as nullable.

lib/helpers.dart

@@ -29,6 +29,7 @@ import 'web.dart';
 
 export 'src/helpers/enums.dart';
 export 'src/helpers/events/events.dart';
+export 'src/helpers/events/providers.dart';
 export 'src/helpers/events/streams.dart' show EventStreamProvider;
 export 'src/helpers/extensions.dart';
 export 'src/helpers/http.dart';

lib/src/helpers/events/events.dart

@@ -261,6 +261,9 @@ extension WindowEventGetters on Window {
 
   Stream<KeyboardEvent> get onKeyPress =>
       EventStreamProviders.keyPressEvent.forTarget(this);
+
+  Stream<MessageEvent> get onMessage =>
+      EventStreamProviders.messageEvent.forTarget(this);
 }
 
 extension ElementCustomEvents on Element {