[Web] Update modifier state when Meta key is seen as Process key (#50779

)

## Description

On Web, browsers can emit key events with a logical key sets to `Process` when the physical key is MetaLeft. Because the modifier state is 0 despite Meta key being pressed this will trigger an assert.
This PR adds some logic for this specific case. Maybe a more slightly broader solution will be needed (using the same logic for all modifiers ?). I focused on MetaLeft because it was directly reported on  flutter/flutter#141186.

## Related Issue

Fixes flutter/flutter#141186.

## Tests

Adds 1 test.

lib/web_ui/lib/src/engine/raw_keyboard.dart

@@ -123,6 +123,10 @@ class RawKeyboard {
       } else if (event.key == 'Meta' && operatingSystem == OperatingSystem.linux) {
         // On Chrome Linux, metaState can be wrong when a Meta key is pressed.
         _lastMetaState |= _modifierMeta;
+      } else if (event.code == 'MetaLeft' && event.key == 'Process') {
+        // When Meta key is pressed, browsers can emit an event whose key is 'Process'.
+        // See https://github.com/flutter/flutter/issues/141186.
+        _lastMetaState |= _modifierMeta;
       }
     }
     final Map<String, dynamic> eventData = <String, dynamic>{

lib/web_ui/test/engine/raw_keyboard_test.dart

@@ -153,7 +153,7 @@ void testMain() {
     });
 
     // Regression test for https://github.com/flutter/flutter/issues/125672.
-    test('updates meta state for Meta key and wrong DOM event metaKey value', () {
+    test('updates meta state for Meta key and wrong DOM event metaKey value (Linux)', () {
       RawKeyboard.initialize();
 
       Map<String, dynamic>? dataReceived;
@@ -181,6 +181,38 @@ void testMain() {
       RawKeyboard.instance!.dispose();
     }, skip: operatingSystem != OperatingSystem.linux);
 
+    // Regression test for https://github.com/flutter/flutter/issues/141186.
+    test('updates meta state for Meta key seen as "Process" key', () {
+      RawKeyboard.initialize();
+
+      Map<String, dynamic>? dataReceived;
+      ui.PlatformDispatcher.instance.onPlatformMessage = (String channel, ByteData? data,
+          ui.PlatformMessageResponseCallback? callback) {
+        dataReceived = const JSONMessageCodec().decodeMessage(data) as Map<String, dynamic>?;
+      };
+
+      // Purposely send a DOM event where Meta key is pressed but event.metaKey is not set to true.
+      // This can happen when the Meta key is seen as the 'Process' key.
+      final DomKeyboardEvent event = dispatchKeyboardEvent(
+        'keydown',
+        key: 'Process',
+        code: 'MetaLeft',
+        location: 1,
+        keyCode: 229,
+      );
+      expect(event.defaultPrevented, isFalse);
+      expect(dataReceived, <String, dynamic>{
+        'type': 'keydown',
+        'keymap': 'web',
+        'code': 'MetaLeft',
+        'key': 'Process',
+        'location': 1,
+        'metaState': 0x8,
+        'keyCode': 229,
+      });
+      RawKeyboard.instance!.dispose();
+    });
+
     test('dispatches repeat events', () {
       RawKeyboard.initialize();