Make SnackBar animate itself.

packages/flutter/example/stocks/lib/stock_home.dart

@@ -51,8 +51,8 @@ class StockHome extends StatefulComponent {
   bool _isSearching = false;
   String _searchQuery;
 
-  SnackBarStatus _snackBarStatus;
-  bool _isSnackBarShowing = false; // Should it be showing?
+  SnackBarStatus _snackBarStatus = SnackBarStatus.inactive;
+  bool _isSnackBarShowing = false;
 
   void _handleSearchBegin() {
     navigator.pushState(this, (_) {

packages/flutter/lib/widgets/drawer.dart

@@ -46,16 +46,6 @@ enum DrawerStatus {
 
 typedef void DrawerStatusChangedCallback(DrawerStatus status);
 
-// TODO(mpcomplete): find a better place for this.
-class AnimatedColor extends AnimatedType<Color> {
-  AnimatedColor(Color begin, { Color end, Curve curve: linear })
-    : super(begin, end: end, curve: curve);
-
-  void setFraction(double t) {
-    value = lerpColor(begin, end, t);
-  }
-}
-
 class Drawer extends AnimatedComponent {
   Drawer({
     String key,

packages/flutter/lib/widgets/snack_bar.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:sky/animation/animated_value.dart';
 import 'package:sky/animation/animation_performance.dart';
 import 'package:sky/painting/text_style.dart';
 import 'package:sky/theme/typography.dart' as typography;
@@ -69,11 +70,11 @@ class SnackBar extends AnimatedComponent {
     }
   }
 
-  AnimatedType<Point> _position;
+  AnimatedValue<Point> _position;
   AnimationPerformance _performance;
 
   void initState() {
-    _position = new AnimatedType<Point>(new Point(0.0, 50.0), end: Point.origin);
+    _position = new AnimatedValue<Point>(new Point(0.0, 50.0), end: Point.origin);
     _performance = new AnimationPerformance()
       ..duration = _kSlideInDuration
       ..variable = _position