Remove the pointless second argument to animate() in AnimatedValue.

- Rename animate() to watch().

- Fix Toggleable to actually be animated (previously, it was
  essentially luck that let it be animated -- it was piggy-backing on
  the splash, I think).

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1216533003.

sdk/lib/widgets/animated_component.dart

@@ -7,12 +7,9 @@ import 'dart:async';
 import '../animation/animated_value.dart';
 import 'basic.dart';
 
-typedef void SetterFunction(double value);
-
 class _AnimationEntry {
-  _AnimationEntry(this.value, this.setter);
+  _AnimationEntry(this.value);
   final AnimatedValue value;
-  final SetterFunction setter;
   StreamSubscription<double> subscription;
 }
 
@@ -24,16 +21,19 @@ abstract class AnimatedComponent extends Component {
 
   List<_AnimationEntry> _animatedFields = new List<_AnimationEntry>();
 
-  animate(AnimatedValue value, SetterFunction setter) {
+  watch(AnimatedValue value) {
     assert(!mounted);
-    setter(value.value);
-    _animatedFields.add(new _AnimationEntry(value, setter));
+    // TODO(ianh): we really should assert that we're not doing this
+    // in the constructor since doing it there is pointless and
+    // expensive, since we'll be doing it for every copy of the object
+    // even though only the first one will use it (since we're
+    // stateful, the others will all be discarded early).
+    _animatedFields.add(new _AnimationEntry(value));
   }
 
   void didMount() {
     for (_AnimationEntry entry in _animatedFields) {
       entry.subscription = entry.value.onValueChanged.listen((_) {
-        entry.setter(entry.value.value);
         scheduleBuild();
       });
     }

sdk/lib/widgets/drawer.dart

@@ -114,9 +114,7 @@ class Drawer extends AnimatedComponent {
     this.children,
     this.level: 0
   }) : super(key: key) {
-    animate(controller.position, (double value) {
-      _position = value;
-    });
+    watch(controller.position);
   }
 
   List<Widget> children;
@@ -130,13 +128,11 @@ class Drawer extends AnimatedComponent {
     super.syncFields(source);
   }
 
-  double _position;
-
   Widget build() {
     Matrix4 transform = new Matrix4.identity();
-    transform.translate(_position);
+    transform.translate(controller.position.value);
 
-    double scaler = _position / _kWidth + 1;
+    double scaler = controller.position.value / _kWidth + 1;
     Color maskColor = new Color.fromARGB((0x7F * scaler).floor(), 0, 0, 0);
 
     var mask = new Listener(

sdk/lib/widgets/popup_menu.dart

@@ -60,10 +60,7 @@ class PopupMenu extends AnimatedComponent {
       backgroundColor: Grey[50],
       borderRadius: 2.0,
       boxShadow: shadows[level]));
-
-    animate(controller.position, (double value) {
-      _position = value;
-    });
+    watch(controller.position);
   }
 
   PopupMenuController controller;
@@ -78,16 +75,15 @@ class PopupMenu extends AnimatedComponent {
     super.syncFields(source);
   }
 
-  double _position;
   BoxPainter _painter;
 
   double _opacityFor(int i) {
-    if (_position == null || _position == 1.0)
+    if (controller.position.value == null || controller.position.value == 1.0)
       return 1.0;
     double unit = 1.0 / items.length;
     double duration = 1.5 * unit;
     double start = i * unit;
-    return math.max(0.0, math.min(1.0, (_position - start) / duration));
+    return math.max(0.0, math.min(1.0, (controller.position.value - start) / duration));
   }
 
   Widget build() {
@@ -98,12 +94,12 @@ class PopupMenu extends AnimatedComponent {
     }));
 
     return new Opacity(
-      opacity: math.min(1.0, _position * 3.0),
+      opacity: math.min(1.0, controller.position.value * 3.0),
       child: new ShrinkWrapWidth(
         child: new CustomPaint(
           callback: (sky.Canvas canvas, Size size) {
-            double width = math.min(size.width, size.width * (0.5 + _position * 2.0));
-            double height = math.min(size.height, size.height * _position * 1.5);
+            double width = math.min(size.width, size.width * (0.5 + controller.position.value * 2.0));
+            double height = math.min(size.height, size.height * controller.position.value * 1.5);
             _painter.paint(canvas, new Rect.fromLTRB(size.width - width, 0.0, width, height));
           },
           child: new Container(

sdk/lib/widgets/toggleable.dart

@@ -21,6 +21,7 @@ abstract class Toggleable extends AnimatedComponent {
     this.onChanged
   }) : super(key: key) {
     toggleAnimation = new AnimatedValue(value ? 1.0 : 0.0);
+    watch(toggleAnimation);
   }
 
   bool value;