Roll Observatory packages and add a roll script

packages/observe/README.md

+# observe
+
+Support for marking objects as observable, and getting notifications when those
+objects are mutated.
+
+**Warning:** This library is experimental, and APIs are subject to change.
+
+This library is used to observe changes to [Observable][] types. It also
+has helpers to make implementing and using [Observable][] objects easy.
+
+You can provide an observable object in two ways. The simplest way is to
+use dirty checking to discover changes automatically:
+
+```dart
+import 'package:observe/observe.dart';
+import 'package:observe/mirrors_used.dart'; // for smaller code
+
+class Monster extends Unit with Observable {
+  @observable int health = 100;
+
+  void damage(int amount) {
+    print('$this takes $amount damage!');
+    health -= amount;
+  }
+
+  toString() => 'Monster with $health hit points';
+}
+
+main() {
+  var obj = new Monster();
+  obj.changes.listen((records) {
+    print('Changes to $obj were: $records');
+  });
+  // No changes are delivered until we check for them
+  obj.damage(10);
+  obj.damage(20);
+  print('dirty checking!');
+  Observable.dirtyCheck();
+  print('done!');
+}
+```
+
+A more sophisticated approach is to implement the change notification
+manually. This avoids the potentially expensive [Observable.dirtyCheck][]
+operation, but requires more work in the object:
+
+```dart
+import 'package:observe/observe.dart';
+import 'package:observe/mirrors_used.dart'; // for smaller code
+
+class Monster extends Unit with ChangeNotifier {
+  int _health = 100;
+  @reflectable get health => _health;
+  @reflectable set health(val) {
+    _health = notifyPropertyChange(#health, _health, val);
+  }
+
+  void damage(int amount) {
+    print('$this takes $amount damage!');
+    health -= amount;
+  }
+
+  toString() => 'Monster with $health hit points';
+}
+
+main() {
+  var obj = new Monster();
+  obj.changes.listen((records) {
+    print('Changes to $obj were: $records');
+  });
+  // Schedules asynchronous delivery of these changes
+  obj.damage(10);
+  obj.damage(20);
+  print('done!');
+}
+```
+
+**Note**: by default this package uses mirrors to access getters and setters
+marked with `@reflectable`. Dart2js disables tree-shaking if there are any
+uses of mirrors, unless you declare how mirrors are used (via the
+[MirrorsUsed](https://api.dartlang.org/apidocs/channels/stable/#dart-mirrors.MirrorsUsed)
+annotation).
+
+As of version 0.10.0, this package doesn't declare `@MirrorsUsed`. This is
+because we intend to use mirrors for development time, but assume that
+frameworks and apps that use this pacakge will either generate code that
+replaces the use of mirrors, or add the `@MirrorsUsed` declaration
+themselves.  For convenience, you can import
+`package:observe/mirrors_used.dart` as shown on the first example above.
+That will add a `@MirrorsUsed` annotation that preserves properties and
+classes labeled with `@reflectable` and properties labeled with
+`@observable`.
+
+If you are using the `package:observe/mirrors_used.dart` import, you can
+also make use of `@reflectable` on your own classes and dart2js will
+preserve all of its members for reflection.
+
+[Tools](https://www.dartlang.org/polymer-dart/) exist to convert the first
+form into the second form automatically, to get the best of both worlds.
+
+[Observable]: http://www.dartdocs.org/documentation/observe/latest/index.html#observe/observe.Observable
+[Observable.dirtyCheck]: http://www.dartdocs.org/documentation/observe/latest/index.html#observe/observe.Observable@id_dirtyCheck