loadfontfromlist should send fontchange message to framework

lib/ui/text.dart

@@ -2123,7 +2123,20 @@ class ParagraphBuilder extends NativeFieldWrapperClass2 {
 Future<void> loadFontFromList(Uint8List list, {String fontFamily}) {
   return _futurize(
     (_Callback<void> callback) => _loadFontFromList(list, callback, fontFamily)
-  );
+  ).then((_) => _sendFontChangeMessage());
+}
+
+final ByteData _fontChangeMessage = utf8.encoder.convert(
+  json.encode(<String, dynamic>{'type': 'fontsChange'})
+).buffer.asByteData();
+
+FutureOr<void> _sendFontChangeMessage() async {
+  if (window.onPlatformMessage != null)
+    window.onPlatformMessage(
+      'flutter/system',
+      _fontChangeMessage,
+      (_) {},
+    );
 }
 
 String _loadFontFromList(Uint8List list, _Callback<void> callback, String fontFamily) native 'loadFontFromList';

lib/web_ui/lib/src/ui/text.dart

@@ -1498,5 +1498,18 @@ abstract class ParagraphBuilder {
 /// * `fontFamily`: The family name used to identify the font in text styles.
 ///  If this is not provided, then the family name will be extracted from the font file.
 Future<void> loadFontFromList(Uint8List list, {String fontFamily}) {
-  return _fontCollection.loadFontFromList(list, fontFamily: fontFamily);
+  return _fontCollection.loadFontFromList(list, fontFamily: fontFamily).then(
+    (_) => _sendFontChangeMessage()
+  );
+}
+
+final ByteData _fontChangeMessage = engine.JSONMessageCodec().encodeMessage(<String, dynamic>{'type': 'fontsChange'});
+
+FutureOr<void> _sendFontChangeMessage() async {
+  if (window.onPlatformMessage != null)
+    window.onPlatformMessage(
+      'flutter/system',
+      _fontChangeMessage,
+      (_) {},
+    );
 }

lib/web_ui/test/text/font_loading_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:convert';
 import 'dart:html' as html;
 import 'dart:typed_data';
 
@@ -36,7 +37,7 @@ Future<void> main() async {
       expect(_containsFontFamily('Blehm'), true);
     });
 
-    test('loads font should clear measurement caches', () async {
+    test('loading font should clear measurement caches', () async {
       final ui.ParagraphStyle style = ui.ParagraphStyle();
       final ui.ParagraphBuilder builder = ui.ParagraphBuilder(style);
       final ui.ParagraphConstraints constraints = ui.ParagraphConstraints(width: 30.0);
@@ -58,6 +59,26 @@ Future<void> main() async {
       expect(_containsFontFamily('Blehm'), true);
       expect(TextMeasurementService.rulerManager.rulers.length, 0);
     });
+
+    test('loading font should send font change message', () async {
+      final ui.PlatformMessageCallback oldHandler = ui.window.onPlatformMessage;
+      String actualName;
+      String message;
+      window.onPlatformMessage = (String name, ByteData data, ui.PlatformMessageResponseCallback callback) {
+        actualName = name;
+        final buffer = data.buffer;
+        final Uint8List list = buffer.asUint8List(data.offsetInBytes, data.lengthInBytes);
+        message = utf8.decode(list);
+      };
+      final html.HttpRequest response = await html.HttpRequest.request(
+        _testFontUrl,
+        responseType: 'arraybuffer');
+      await ui.loadFontFromList(Uint8List.view(response.response),
+        fontFamily: 'Blehm');
+      window.onPlatformMessage = oldHandler;
+      expect(actualName, 'flutter/system');
+      expect(message, '{"type":"fontsChange"}');
+    });
   });
 }
 

testing/dart/text_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:convert';
+import 'dart:typed_data';
 import 'dart:ui';
 
 import 'package:test/test.dart';
@@ -79,4 +81,21 @@ void main() {
       expect(const TextRange(start: 0, end: 5).textInside('hello'), equals('hello'));
     });
   });
+  group('loadFontFromList', () {
+    test('will send platform message after font is loaded', () async {
+      final PlatformMessageCallback oldHandler = window.onPlatformMessage;
+      String actualName;
+      String message;
+      window.onPlatformMessage = (String name, ByteData data, PlatformMessageResponseCallback callback) {
+        actualName = name;
+        final Uint8List list = data.buffer.asUint8List(data.offsetInBytes, data.lengthInBytes);
+        message = utf8.decode(list);
+      };
+      final Uint8List fontData = Uint8List(0);
+      await loadFontFromList(fontData, fontFamily: 'fake');
+      window.onPlatformMessage = oldHandler;
+      expect(actualName, 'flutter/system');
+      expect(message, '{"type":"fontsChange"}');
+    });
+  });
 }