removed fonts clear and factory constructor

Author: alanwutang11

lib/web_ui/lib/src/engine/safe_browser_api.dart

@@ -134,10 +134,6 @@ num? parseFloat(String source) {
   return result;
 }
 
-final bool supportsFontsClearApi =
-    js_util.hasProperty(domDocument, 'fonts') &&
-        js_util.hasProperty(domDocument.fonts!, 'clear');
-
 /// Used to decide if the browser tab still has the focus.
 ///
 /// This information is useful for deciding on the blur behavior.

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

@@ -102,17 +102,14 @@ class HtmlFontCollection implements FontCollection {
   void clear() {
     _assetFontManager = null;
     _testFontManager = null;
-    if (supportsFontsClearApi) {
-      domDocument.fonts!.clear();
-    }
+    domDocument.fonts!.clear();
   }
 }
 
 /// Manages a collection of fonts and ensures they are loaded.
 class FontManager {
-  factory FontManager() = FontManager._;
 
-  FontManager._();
+  FontManager();
 
   /// Fonts that started the downloading process. Once the fonts have downloaded
   /// without error, they are moved to [_downloadedFonts]. Those fonts