Moving background animation ticking from LayerTreeHostImpl into the Scheduler.

cc/animation/layer_animation_controller.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/animation/layer_animation_controller.h"
 
 #include <algorithm>
 #include <vector>
 
 #include "cc/animation/animation.h"
@@ skipping 194 matching lines @@
         NOTREACHED();
     }
   }
 }
 
 void LayerAnimationController::UpdateState(bool start_ready_animations,
                                            AnimationEventsVector* events) {
   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);
 
   MarkFinishedAnimations(last_tick_time_);
   MarkAnimationsForDeletion(last_tick_time_, events);
 
   if (needs_to_start_animations_ && start_ready_animations) {
     StartAnimations(last_tick_time_);
     PromoteStartedAnimations(last_tick_time_, events);
   }
@@ skipping 803 matching lines @@
         value_observers_);
     LayerAnimationValueObserver* obs;
     while ((obs = it.GetNext()) != nullptr)
       if (obs->IsActive())
         return true;
   }
   return false;
 }
 
 }  // namespace cc