Add check for iOS/MacOS for target platform (#56081)

packages/flutter/lib/src/foundation/_platform_web.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:html' as html;
 import 'platform.dart' as platform;
 
 /// The dart:html implementation of [platform.defaultTargetPlatform].
@@ -9,8 +10,21 @@ platform.TargetPlatform get defaultTargetPlatform {
   // To getter a better guess at the targetPlatform we need to be able to
   // reference the window, but that won't be availible until we fix the
   // platforms configuration for Flutter.
-  platform.TargetPlatform result = platform.TargetPlatform.android;
+  platform.TargetPlatform result = _browserPlatform();
   if (platform.debugDefaultTargetPlatformOverride != null)
     result = platform.debugDefaultTargetPlatformOverride;
   return result;
 }
+
+platform.TargetPlatform _browserPlatform() {
+  final String navigatorPlatform = html.window.navigator.platform.toLowerCase();
+  if (navigatorPlatform.startsWith('mac')) {
+    return platform.TargetPlatform.macOS;
+  }
+  if (navigatorPlatform.contains('iphone') ||
+      navigatorPlatform.contains('ipad') ||
+      navigatorPlatform.contains('ipod')) {
+    return platform.TargetPlatform.iOS;
+  }
+  return platform.TargetPlatform.android;
+}