fix(animation): correct broken build http://dartbug.com/17634

Author: mhevery

test/animate/css_animate_spec.dart

@@ -111,7 +111,7 @@ class MockAnimationLoop extends Mock implements AnimationLoop {
 
   List<LoopedAnimation> animations = [];
 
-  play(Animation animation) {
+  play(LoopedAnimation animation) {
     animations.add(animation);
   }
 
@@ -128,4 +128,4 @@ class MockAnimationLoop extends Mock implements AnimationLoop {
   }
 
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
-}
+}