Adds Roboto as a global font fallback in CanvasKit (#23928)

lib/web_ui/lib/src/engine/canvaskit/fonts.dart

@@ -28,7 +28,7 @@ class SkiaFontCollection {
   final Map<String, List<SkTypeface>> familyToTypefaceMap =
       <String, List<SkTypeface>>{};
 
-  final List<String> globalFontFallbacks = <String>[];
+  final List<String> globalFontFallbacks = <String>['Roboto'];
 
   final Map<String, int> _fontFallbackCounts = <String, int>{};
 
@@ -178,6 +178,7 @@ class SkiaFontCollection {
   void debugResetFallbackFonts() {
     _registeredFallbackFonts.clear();
     globalFontFallbacks.clear();
+    globalFontFallbacks.add('Roboto');
     _fontFallbackCounts.clear();
   }
 

lib/web_ui/lib/src/engine/canvaskit/text.dart

@@ -814,9 +814,7 @@ enum _ParagraphCommandType {
 List<String> _getEffectiveFontFamilies(String? fontFamily,
     [List<String>? fontFamilyFallback]) {
   List<String> fontFamilies = <String>[];
-  if (fontFamily == null) {
-    fontFamilies.add('Roboto');
-  } else {
+  if (fontFamily != null) {
     fontFamilies.add(fontFamily);
   }
   if (fontFamilyFallback != null &&

lib/web_ui/test/canvaskit/fallback_fonts_golden_test.dart

@@ -51,6 +51,10 @@ void testMain() {
       ui.window.onPlatformMessage = savedCallback;
     });
 
+    test('Roboto is always a fallback font', () {
+      expect(skiaFontCollection.globalFontFallbacks, contains('Roboto'));
+    });
+
     test('will download Noto Naskh Arabic if Arabic text is added', () async {
       final Completer<void> fontChangeCompleter = Completer<void>();
       // Intercept the system font change message.
@@ -83,7 +87,7 @@ void testMain() {
 }
 ''';
 
-      expect(skiaFontCollection.globalFontFallbacks, isEmpty);
+      expect(skiaFontCollection.globalFontFallbacks, ['Roboto']);
 
       // Creating this paragraph should cause us to start to download the
       // fallback font.
@@ -123,7 +127,7 @@ void testMain() {
               'https://fonts.googleapis.com/css2?family=Noto+Naskh+Arabic+UI'] =
           'invalid CSS... this should cause our parser to fail';
 
-      expect(skiaFontCollection.globalFontFallbacks, isEmpty);
+      expect(skiaFontCollection.globalFontFallbacks, ['Roboto']);
 
       // Creating this paragraph should cause us to start to download the
       // fallback font.
@@ -136,7 +140,7 @@ void testMain() {
       await Future<void>.delayed(Duration.zero);
 
       expect(notoDownloadQueue.isPending, isFalse);
-      expect(skiaFontCollection.globalFontFallbacks, isEmpty);
+      expect(skiaFontCollection.globalFontFallbacks, ['Roboto']);
     });
     // TODO: https://github.com/flutter/flutter/issues/60040
   }, skip: isIosSafari);