[observe] use consistent comment style

pkg/observe/lib/src/metadata.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library observe.src.metadata;
 
-/**
- * Use `@observable` to make a field automatically observable, or to indicate
- * that a property is observable.
- */
+/// Use `@observable` to make a field automatically observable, or to indicate
+/// that a property is observable.
 const ObservableProperty observable = const ObservableProperty();
 
-/**
- * An annotation that is used to make a property observable.
- * Normally this is used via the [observable] constant, for example:
- *
- *     class Monster {
- *       @observable int health;
- *     }
- *
- * If needed, you can subclass this to create another annotation that will also
- * be treated as observable.
- */
+/// An annotation that is used to make a property observable.
+/// Normally this is used via the [observable] constant, for example:
+///
+///     class Monster {
+///       @observable int health;
+///     }
+///
+/// If needed, you can subclass this to create another annotation that will also
+/// be treated as observable.
 // Note: observable properties imply reflectable.
 class ObservableProperty {
   const ObservableProperty();
 }
 
 
-/**
- * Use `@reflectable` to make a type or member available to reflection in the
- * observe package. This is necessary to make the member visible to
- * [PathObserver], or similar systems, once the code is deployed.
- */
+/// Use `@reflectable` to make a type or member available to reflection in the
+/// observe package. This is necessary to make the member visible to
+/// [PathObserver], or similar systems, once the code is deployed.
 const Reflectable reflectable = const Reflectable();
 
-/**
- * An annotation that is used to make a type or member reflectable. This makes
- * it available to [PathObserver] at runtime. For example:
- *
- *     @reflectable
- *     class Monster extends ChangeNotifier {
- *       int _health;
- *       int get health => _health;
- *       ...
- *     }
- *     ...
- *       // This will work even if the code has been tree-shaken/minified:
- *       final monster = new Monster();
- *       new PathObserver(monster, 'health').changes.listen(...);
- */
+/// An annotation that is used to make a type or member reflectable. This makes
+/// it available to [PathObserver] at runtime. For example:
+///
+///     @reflectable
+///     class Monster extends ChangeNotifier {
+///       int _health;
+///       int get health => _health;
+///       ...
+///     }
+///     ...
+///       // This will work even if the code has been tree-shaken/minified:
+///       final monster = new Monster();
+///       new PathObserver(monster, 'health').changes.listen(...);
 class Reflectable {
   const Reflectable();
 }