Use AnimatedContainer for card_collection.dart.

sky/sdk/lib/animation/animation_performance.dart

Index: sky/sdk/lib/animation/animation_performance.dart
diff --git a/sky/sdk/lib/animation/animation_performance.dart b/sky/sdk/lib/animation/animation_performance.dart
index 829f9e55ad8ddba46d3df9965d73bc4e0923db21..e68037d4611d14aebc6870ca3607508d949f8a2b 100644
--- a/sky/sdk/lib/animation/animation_performance.dart
+++ b/sky/sdk/lib/animation/animation_performance.dart
@@ -28,6 +28,15 @@ class AnimatedType<T extends dynamic> extends AnimatedVariable {
   }
 }
 
+class AnimatedList extends AnimatedVariable {
+  List<AnimatedVariable> variables;
+  AnimatedList(this.variables);
+  void setFraction(double t) {
+    for (AnimatedVariable variable in variables)
+      variable.setFraction(t);
+  }
+}
+
 // This class manages a "performance" - a collection of values that change
 // based on a timeline. For example, a performance may handle an animation
 // of a menu opening by sliding and fading in (changing Y value and opacity)