fix dart docs for build (#67479)

packages/flutter_web_plugins/lib/flutter_web_plugins.dart

@@ -14,7 +14,7 @@
 /// See also:
 ///
 ///  * [How to Write a Flutter Web Plugin](https://medium.com/flutter/how-to-write-a-flutter-web-plugin-5e26c689ea1), a Medium article
-///    describing how the [url_launcher] package was created using [flutter_web_plugins].
+///    describing how the `url_launcher` package was created using [flutter_web_plugins].
 library flutter_web_plugins;
 
 export 'src/plugin_event_channel.dart';

packages/flutter_web_plugins/lib/src/plugin_event_channel.dart

@@ -28,12 +28,12 @@ import 'plugin_registry.dart';
 ///
 /// The first method is `listen`. When called, it begins forwarding
 /// messages to the framework side when they are added to the
-/// [controller]. This triggers the [onListen] callback on the
-/// [controller].
+/// [controller]. This triggers the [StreamController.onListen] callback
+/// on the [controller].
 ///
 /// The other method is `cancel`. When called, it stops forwarding
-/// events to the framework. This triggers the [onCancel] callback on
-/// the [controller].
+/// events to the framework. This triggers the [StreamController.onCancel]
+/// callback on the [controller].
 ///
 /// Events added to the [controller] when the framework is not
 /// subscribed are silently discarded.