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

cc/animation/layer_animation_controller.h

 // 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.
 
 #ifndef CC_ANIMATION_LAYER_ANIMATION_CONTROLLER_H_
 #define CC_ANIMATION_LAYER_ANIMATION_CONTROLLER_H_
 
 #include <bitset>
 #include <memory>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "base/observer_list.h"
 #include "base/time/time.h"
 #include "cc/animation/animation.h"
 #include "cc/animation/layer_animation_event_observer.h"
 #include "cc/animation/target_property.h"
 #include "cc/base/cc_export.h"
 #include "ui/gfx/geometry/scroll_offset.h"
 #include "ui/gfx/transform.h"
 
 namespace gfx {
 class BoxF;
@@ skipping 89 matching lines @@
 
   void set_needs_active_value_observations(
       bool needs_active_value_observations) {
     needs_active_value_observations_ = needs_active_value_observations;
   }
   void set_needs_pending_value_observations(
       bool needs_pending_value_observations) {
     needs_pending_value_observations_ = needs_pending_value_observations;
   }
 
-  void AddEventObserver(LayerAnimationEventObserver* observer);
-  void RemoveEventObserver(LayerAnimationEventObserver* observer);
+  void SetEventObserver(LayerAnimationEventObserver* observer);
 
   void set_value_provider(LayerAnimationValueProvider* provider) {
     value_provider_ = provider;
   }
 
   void remove_value_provider(LayerAnimationValueProvider* provider) {
     if (value_provider_ == provider)
       value_provider_ = nullptr;
   }
 
@@ skipping 26 matching lines @@
 
   // Sets |start_scale| to the maximum of starting animation scale along any
   // dimension at any destination in active animations. Returns false if the
   // starting scale cannot be computed.
   bool AnimationStartScale(ObserverType observer_type,
                            float* start_scale) const;
 
   // Sets |max_scale| to the maximum scale along any dimension at any
   // destination in active animations. Returns false if the maximum scale cannot
   // be computed.
-  bool MaximumTargetScale(ObserverType event_observers_,
-                          float* max_scale) const;
+  bool MaximumTargetScale(ObserverType observer_type, float* max_scale) const;
 
   // When a scroll animation is removed on the main thread, its compositor
   // thread counterpart continues producing scroll deltas until activation.
   // These scroll deltas need to be cleared at activation, so that the active
   // layer's scroll offset matches the offset provided by the main thread
   // rather than a combination of this offset and scroll deltas produced by
   // the removed animation. This is to provide the illusion of synchronicity to
   // JS that simultaneously removes an animation and sets the scroll offset.
   bool scroll_offset_animation_was_interrupted() const {
     return scroll_offset_animation_was_interrupted_;
@@ skipping 61 matching lines @@
 
   AnimationHost* host_;
   int id_;
   std::vector<std::unique_ptr<Animation>> animations_;
 
   // This is used to ensure that we don't spam the animation host.
   bool is_active_;
 
   base::TimeTicks last_tick_time_;
 
-  base::ObserverList<LayerAnimationEventObserver> event_observers_;
+  LayerAnimationEventObserver* event_observer_;
   LayerAnimationValueObserver* value_observer_;
   LayerAnimationValueProvider* value_provider_;
   AnimationDelegate* layer_animation_delegate_;
 
   bool needs_active_value_observations_;
   bool needs_pending_value_observations_;
 
   // Only try to start animations when new animations are added or when the
   // previous attempt at starting animations failed to start all animations.
   bool needs_to_start_animations_;
 
   bool scroll_offset_animation_was_interrupted_;
 
   bool potentially_animating_transform_for_active_observers_;
   bool potentially_animating_transform_for_pending_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerAnimationController);
 };
 
 }  // namespace cc
 
 #endif  // CC_ANIMATION_LAYER_ANIMATION_CONTROLLER_H_