Implement handling of framework-handled key events

lib/web_ui/lib/src/engine/keyboard.dart

@@ -80,11 +80,6 @@ class Keyboard {
     }
 
     final html.KeyboardEvent keyboardEvent = event;
-
-    if (_shouldPreventDefault(event)) {
-      event.preventDefault();
-    }
-
     final String timerKey = keyboardEvent.code!;
 
     // Don't handle synthesizing a keyup event for modifier keys
@@ -132,16 +127,17 @@ class Keyboard {
     };
 
     EnginePlatformDispatcher.instance.invokeOnPlatformMessage('flutter/keyevent',
-        _messageCodec.encodeMessage(eventData), _noopCallback);
-  }
-
-  bool _shouldPreventDefault(html.KeyboardEvent event) {
-    switch (event.key) {
-      case 'Tab':
-        return true;
-      default:
-        return false;
-    }
+      _messageCodec.encodeMessage(eventData), (ByteData? data) {
+        if (data == null) {
+          return;
+        }
+        final Map<String, dynamic> jsonResponse = _messageCodec.decodeMessage(data);
+        if (jsonResponse['handled'] as bool) {
+          // If the framework handled it, then don't propagate it any further.
+          event.preventDefault();
+        }
+      },
+    );
   }
 
   void _synthesizeKeyup(html.KeyboardEvent event) {

lib/web_ui/test/keyboard_test.dart

@@ -226,13 +226,15 @@ void testMain() {
       expect(count, 2);
     });
 
-    test('prevents default when "Tab" is pressed', () {
+    test('prevents default when key is handled by the framework', () {
       Keyboard.initialize();
 
       int count = 0;
       ui.window.onPlatformMessage = (String channel, ByteData data,
           ui.PlatformMessageResponseCallback callback) {
         count += 1;
+        ByteData response = const JSONMessageCodec().encodeMessage(<String, dynamic>{'handled': true});
+        callback(response);
       };
 
       final html.KeyboardEvent event = dispatchKeyboardEvent(
@@ -247,6 +249,29 @@ void testMain() {
       Keyboard.instance.dispose();
     });
 
+    test("Doesn't prevent default when key is not handled by the framework", () {
+      Keyboard.initialize();
+
+      int count = 0;
+      ui.window.onPlatformMessage = (String channel, ByteData data,
+          ui.PlatformMessageResponseCallback callback) {
+        count += 1;
+        ByteData response = const JSONMessageCodec().encodeMessage(<String, dynamic>{'handled': false});
+        callback(response);
+      };
+
+      final html.KeyboardEvent event = dispatchKeyboardEvent(
+        'keydown',
+        key: 'Tab',
+        code: 'Tab',
+      );
+
+      expect(event.defaultPrevented, isFalse);
+      expect(count, 1);
+
+      Keyboard.instance.dispose();
+    });
+
     test('keyboard events should be triggered on text fields', () {
       Keyboard.initialize();
 
@@ -278,6 +303,8 @@ void testMain() {
       ui.window.onPlatformMessage = (String channel, ByteData data,
           ui.PlatformMessageResponseCallback callback) {
         count += 1;
+        ByteData response = const JSONMessageCodec().encodeMessage(<String, dynamic>{'handled': true});
+        callback(response);
       };
 
       useTextEditingElement((html.Element element) {