Revert "Add handling of 'TextInput.clearClient' message from platform to...

Revert "Add handling of 'TextInput.clearClient' message from platform to framework (#35054). (#35100)" (#39523)

This reverts commit 324fe201.

packages/flutter/lib/src/services/text_input.dart

@@ -632,7 +632,7 @@ abstract class TextInputClient {
 /// See also:
 ///
 ///  * [TextInput.attach]
-class TextInputConnection with ChangeNotifier {
+class TextInputConnection {
   TextInputConnection._(this._client)
     : assert(_client != null),
       _id = _nextId++;
@@ -667,19 +667,12 @@ class TextInputConnection with ChangeNotifier {
   void close() {
     if (attached) {
       SystemChannels.textInput.invokeMethod<void>('TextInput.clearClient');
-      _onConnectionClosed();
-      _clientHandler._scheduleHide();
+      _clientHandler
+        .._currentConnection = null
+        .._scheduleHide();
     }
     assert(!attached);
   }
-
-  /// Clear out the current text input connection.
-  ///
-  /// Call this method when the current text input connection has cleared.
-  void _onConnectionClosed() {
-    _clientHandler._currentConnection = null;
-    notifyListeners();
-  }
 }
 
 TextInputAction _toTextInputAction(String action) {
@@ -760,9 +753,6 @@ class _TextInputClientHandler {
       case 'TextInputClient.updateFloatingCursor':
         _currentConnection._client.updateFloatingCursor(_toTextPoint(_toTextCursorAction(args[1]), args[2]));
         break;
-      case 'TextInputClient.onConnectionClosed':
-        _currentConnection._onConnectionClosed();
-        break;
       default:
         throw MissingPluginException();
     }

packages/flutter/test/services/text_input_test.dart

@@ -88,44 +88,5 @@ void main() {
       expect(signed.hashCode == signedDecimal.hashCode, false);
       expect(decimal.hashCode == signedDecimal.hashCode, false);
     });
-
-    test('The framework TextInputConnection closes when the platform loses its input connection', () async {
-      // Assemble a TextInputConnection so we can verify its change in state.
-      final TextInputClient client = NoOpTextInputClient();
-      const TextInputConfiguration configuration = TextInputConfiguration();
-      final TextInputConnection textInputConnection = TextInput.attach(client, configuration);
-
-      // Verify that TextInputConnection think its attached to a client. This is
-      // an intermediate verification of expected state.
-      expect(textInputConnection.attached, true);
-
-      // Pretend that the platform has lost its input connection.
-      final ByteData messageBytes = const JSONMessageCodec().encodeMessage(
-          <String, dynamic>{
-            'args': <dynamic>[1],
-            'method': 'TextInputClient.onConnectionClosed',
-          }
-      );
-      ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage(
-        'flutter/textinput',
-        messageBytes,
-        (ByteData _) {},
-      );
-
-      // Verify that textInputConnection no longer think its attached to an input
-      // connection. This is the critical verification of this test.
-      expect(textInputConnection.attached, false);
-    });
   });
 }
-
-class NoOpTextInputClient extends TextInputClient {
-  @override
-  void performAction(TextInputAction action) {}
-
-  @override
-  void updateEditingValue(TextEditingValue value) {}
-
-  @override
-  void updateFloatingCursor(RawFloatingCursorPoint point) {}
-}
\ No newline at end of file