CC Animation: Rework iterations over players to use the range-based for loop.

cc/trees/layer_tree_host_unittest_animation.cc

Index: cc/trees/layer_tree_host_unittest_animation.cc
diff --git a/cc/trees/layer_tree_host_unittest_animation.cc b/cc/trees/layer_tree_host_unittest_animation.cc
index 44f7d83f7b6a7de0247a7305f6225bcd8156f957..f7d1536acda64a0c1a8457c3eeb8cbc6bb5de2b3 100644
--- a/cc/trees/layer_tree_host_unittest_animation.cc
+++ b/cc/trees/layer_tree_host_unittest_animation.cc
@@ -858,10 +858,7 @@ class LayerTreeHostAnimationTestScrollOffsetAnimationAdjusted
             layer->element_id());
     DCHECK(element_animations);
     DCHECK(element_animations->players_list().might_have_observers());
-
-    ElementAnimations::PlayersList::Iterator it(
-        &element_animations->players_list());
-    AnimationPlayer* player = it.GetNext();
+    AnimationPlayer* player = &*element_animations->players_list().begin();
     DCHECK(player);
     return *player;
   }