follow up for #25578, add `@checked` to package:meta

CHANGELOG.md

 ## 1.20.0
 
 ### Dart VM
 
 * We have improved the way that the VM locates the native code library for a
   native extension (e.g. `dart-ext:` import). We have updated this
   [article on native extensions](https://www.dartlang.org/articles/dart-vm/native-extensions)
   to reflect the VM's improved behavior.
 
 ### Core library changes
@@ skipping 21 matching lines @@
     }
     main() {
       // Error because:
       // - if we choose Cup<num> it is not assignable to `cOfInt`,
       // - if we choose Cup<int> then `n` is not assignable to int.
       num n;
       C<int> cOfInt = new C(n);
     }
     ```
 
+* New feature - use `@checked` to override a method and tighten a parameter
+    type (SDK issue [25578](https://github.com/dart-lang/sdk/issues/25578)).
+
+    ```dart
+    import 'package:meta/meta.dart' show checked;
+    class View {
+      addChild(View v) {}
+    }
+    class MyView extends View {
+      // this override is legal, it will check at runtime if we actually
+      // got a MyView.
+      addChild(@checked MyView v) {}
+    }
+    main() {
+      dynamic mv = new MyView();
+      mv.addChild(new View()); // runtime error
+    }
+    ```
+
 ## 1.19.0
 
 ### Language changes
 
 * The language now allows a trailing comma after the last argument of a call and
  the last parameter of a function declaration. This can make long argument or
  parameter lists easier to maintain, as commas can be left as-is when
  reordering lines. For details, see SDK issue
  [26644](https://github.com/dart-lang/sdk/issues/26644).
 
@@ skipping 1185 matching lines @@
     they will keep the Dart process alive until they time out. This fixes the
     handling of persistent connections. Previously, the client would shut down
     immediately after a request.
 
   * **Breaking change:** `HttpServer` no longer compresses all traffic by
     default. The new `autoCompress` property can be set to `true` to re-enable
     compression.
 
 * `dart:isolate`: `Isolate.spawnUri` added the optional `packageRoot` argument,
   which controls how it resolves `package:` URIs.