Rationalize Dart mojo and sky package structure

sky/framework/components/animated_component.dart

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-import '../animation/animated_value.dart';
-import '../fn.dart';
-import 'dart:mirrors';
-
-abstract class AnimatedComponent extends Component {
-  AnimatedComponent({ Object key }) : super(key: key, stateful: true);
-
-  var _debugAnimatedFields = new Set<Symbol>();
-  bool _debugIsNotYetAnimated(Symbol s) {
-    return _debugAnimatedFields.add(s);
-  }
-
-  animateField(AnimatedValue value, Symbol symbol) {
-    // TODO(rafaelw): Assert symbol is present on |this|, is private and
-    // is over the same parameterized type as the animated value.
-    var mirror = reflect(this);
-    var subscription;
-
-    assert(_debugIsNotYetAnimated(symbol));
-    mirror.setField(symbol, value.value);
-
-    onDidMount(() {
-      subscription = value.onValueChanged.listen((_) {
-        mirror.setField(symbol, value.value);
-        scheduleBuild();
-      });
-    });
-
-    onDidUnmount(() {
-      if (subscription != null) {
-        subscription.cancel();
-        subscription = null;
-      }
-    });
-  }
-}