Moving background animation ticking from LayerTreeHostImpl into the Scheduler.

cc/animation/layer_animation_controller.cc

Index: cc/animation/layer_animation_controller.cc
diff --git a/cc/animation/layer_animation_controller.cc b/cc/animation/layer_animation_controller.cc
index b779a37957a8d165d517e611f0ee37da334bc963..e34fc4a3d1f1c4705548038b97aeefc22b0e697f 100644
--- a/cc/animation/layer_animation_controller.cc
+++ b/cc/animation/layer_animation_controller.cc
@@ -212,7 +212,11 @@ void LayerAnimationController::UpdateState(bool start_ready_animations,
   if (!HasActiveValueObserver())
     return;
 
-  DCHECK(last_tick_time_ != base::TimeTicks());
+  // Animate hasn't been called, this happens if an observer has been added
+  // between the Commit and Draw phases.
+  if (last_tick_time_ == base::TimeTicks())
+    return;
+
   if (start_ready_animations)
     PromoteStartedAnimations(last_tick_time_, events);