Add some TODOs for renaming onTick and onValueChanged.

sky/sdk/lib/framework/animation/animated_value.dart

Index: sky/sdk/lib/framework/animation/animated_value.dart
diff --git a/sky/sdk/lib/framework/animation/animated_value.dart b/sky/sdk/lib/framework/animation/animated_value.dart
index 8eeafa9d019bbf4f9f6a18cb7b54d91a600431a3..071f6926bccbd251e57a5981d84f5ef6e03a495b 100644
--- a/sky/sdk/lib/framework/animation/animated_value.dart
+++ b/sky/sdk/lib/framework/animation/animated_value.dart
@@ -23,6 +23,7 @@ class AnimatedValue {
   // A stream of change in value from |initial|. The stream does not
   // contain the initial value. Consumers should check the initial value via
   // the |value| accessor.
+  // TODO(ianh): Rename this to valueStream once we've landed the fn2 fork
   Stream<double> get onValueChanged => _controller.stream;
 
   double get value => _value;