Add basic web device and run support (#28302)

packages/flutter_tools/lib/src/device.dart

diff --git a/packages/flutter_tools/lib/src/device.dart b/packages/flutter_tools/lib/src/device.dart
index 52a3153..cad682f 100644
--- a/packages/flutter_tools/lib/src/device.dart
+++ b/packages/flutter_tools/lib/src/device.dart
@@ -20,6 +20,7 @@
 import 'linux/linux_device.dart';
 import 'macos/macos_device.dart';
 import 'tester/flutter_tester.dart';
+import 'web/web_device.dart';
 import 'windows/windows_device.dart';
 
 DeviceManager get deviceManager => context[DeviceManager];
@@ -36,7 +37,7 @@
     IOSSimulators(),
     FuchsiaDevices(),
     FlutterTesterDevices(),
-  ] + _conditionalDesktopDevices);
+  ] + _conditionalDesktopDevices + _conditionalWebDevices);
 
   /// Only add desktop devices if the flag is enabled.
   static List<DeviceDiscovery> get _conditionalDesktopDevices {
@@ -47,6 +48,13 @@
     ] : <DeviceDiscovery>[];
   }
 
+  /// Only add web devices if the flag is enabled.
+  static List<DeviceDiscovery> get _conditionalWebDevices {
+    return flutterWebEnabled ? <DeviceDiscovery>[
+      WebDevices(),
+    ] : <DeviceDiscovery>[];
+  }
+
   String _specifiedDeviceId;
 
   /// A user-specified device ID.