First pass on action animations for sprites

sky/sdk/example/game/lib/sprite_box.dart

Index: sky/sdk/example/game/lib/sprite_box.dart
diff --git a/sky/sdk/example/game/lib/sprite_box.dart b/sky/sdk/example/game/lib/sprite_box.dart
index 25598c381ef3b8542730b6992b996bfc660f93cb..aa5d064e2ac05f2274e9d90c3ec8f91df36c9742 100644
--- a/sky/sdk/example/game/lib/sprite_box.dart
+++ b/sky/sdk/example/game/lib/sprite_box.dart
@@ -287,10 +287,21 @@ class SpriteBox extends RenderBox {
     // Print frame rate
     if (_numFrames % 60 == 0) print("delta: $delta fps: $_frameRate");
 
+    _runActions(_rootNode, delta);
     _callUpdate(_rootNode, delta);
     _scheduleTick();
   }
 
+  void _runActions(Node node, double dt) {
+    if (node._actions != null) {
+      node._actions.step(dt);
+    }
+    for (int i = node.children.length - 1; i >= 0; i--) {

[kulakowski, 2015/07/01 22:18:43]

FYI List has a |reversed| property:

for (final Node child in node.children.reversed) {
   _runActions(child, dt);
}

+      Node child = node.children[i];
+      _runActions(child, dt);
+    }
+  }
+
   void _callUpdate(Node node, double dt) {
     node.update(dt);
     for (int i = node.children.length - 1; i >= 0; i--) {