CC Animation: Make LayerAnimationController to have just one event observer.

cc/animation/layer_animation_controller_unittest.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 <stddef.h>
 
 #include "base/memory/ptr_util.h"
 #include "cc/animation/animation.h"
@@ skipping 1219 matching lines @@
   controller_impl->set_value_observer(&dummy_impl);
   controller_impl->set_needs_active_value_observations(true);
 
   FakeLayerAnimationValueObserver dummy;
   scoped_refptr<LayerAnimationController> controller(
       LayerAnimationController::Create(0));
   controller->set_value_observer(&dummy);
   controller->set_needs_active_value_observations(true);
 
   FakeLayerAnimationEventObserver observer;
-  controller->AddEventObserver(&observer);
+  controller->SetEventObserver(&observer);
 
   int animation_id =
       AddOpacityTransitionToController(controller.get(), 1, 0, 1, false);
 
   const TimeTicks start_time = TicksFromSecondsF(123);
   controller->GetAnimation(TargetProperty::OPACITY)->set_start_time(start_time);
 
   controller->PushAnimationUpdatesTo(controller_impl.get());
   controller_impl->ActivateAnimations();
 
   EXPECT_TRUE(controller_impl->GetAnimationById(animation_id));
   EXPECT_EQ(Animation::WAITING_FOR_TARGET_AVAILABILITY,
             controller_impl->GetAnimationById(animation_id)->run_state());
 
   AnimationEvents events;
   controller_impl->Animate(kInitialTickTime);
   controller_impl->UpdateState(true, &events);
 
   // Synchronize the start times.
   EXPECT_EQ(1u, events.events_.size());
   controller->NotifyAnimationStarted(events.events_[0]);
 
   // Validate start time on the event observer.
   EXPECT_EQ(start_time, observer.start_time());
+
+  controller->SetEventObserver(nullptr);
 }
 
 // Tests animations that are waiting for a synchronized start time do not
 // finish.
 TEST(LayerAnimationControllerTest,
      AnimationsWaitingForStartTimeDoNotFinishIfTheyOutwaitTheirFinish) {
   std::unique_ptr<AnimationEvents> events(
       base::WrapUnique(new AnimationEvents));
   FakeLayerAnimationValueObserver dummy;
   scoped_refptr<LayerAnimationController> controller(
@@ skipping 1935 matching lines @@
       TargetProperty::OPACITY, LayerAnimationController::ObserverType::ACTIVE));
   EXPECT_FALSE(controller->IsCurrentlyAnimatingProperty(
       TargetProperty::OPACITY,
       LayerAnimationController::ObserverType::PENDING));
   EXPECT_FALSE(controller->IsCurrentlyAnimatingProperty(
       TargetProperty::OPACITY, LayerAnimationController::ObserverType::ACTIVE));
 }
 
 }  // namespace
 }  // namespace cc