Keep dedicated layers for hiding animation

ash/wm/maximize_mode/workspace_backdrop_delegate.cc

 // Copyright 2014 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 "ash/wm/maximize_mode/workspace_backdrop_delegate.h"
 
 #include "ash/wm/window_animations.h"
 #include "ash/wm/window_util.h"
 #include "base/auto_reset.h"
 #include "ui/aura/window.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/scoped_layer_animation_settings.h"
 #include "ui/views/background.h"
 #include "ui/views/widget/widget.h"
+#include "ui/wm/core/window_animations.h"
 #include "ui/wm/core/window_util.h"
 
 namespace ash {
 
 namespace internal {
 
 namespace {
 
 // The opacity of the backdrop.
 const float kBackdropOpacity = 0.5f;
@@ skipping 16 matching lines @@
   background_->Init(params);
   background_->GetNativeView()->SetName("WorkspaceBackdropDelegate");
   background_->GetNativeView()->layer()->SetColor(SK_ColorBLACK);
   Show();
   RestackBackdrop();
   container_->AddObserver(this);
 }
 
 WorkspaceBackdropDelegate::~WorkspaceBackdropDelegate() {
   container_->RemoveObserver(this);
-  ui::ScopedLayerAnimationSettings settings(
-      background_->GetNativeView()->layer()->GetAnimator());
+  ::wm::ScopedHidingAnimationSettings hiding_settings(
+      background_->GetNativeView());
   background_->Close();
-  settings.AddObserver(::wm::CreateHidingWindowAnimationObserver(
-      background_->GetNativeView()));
   background_->GetNativeView()->layer()->SetOpacity(0.0f);
 }
 
 void WorkspaceBackdropDelegate::OnWindowBoundsChanged(
     aura::Window* window,
     const gfx::Rect& old_bounds,
     const gfx::Rect& new_bounds) {
   // The container size has changed and the layer needs to be adapt to it.
   AdjustToContainerBounds();
 }
@@ skipping 79 matching lines @@
 void WorkspaceBackdropDelegate::Show() {
   background_->GetNativeView()->layer()->SetOpacity(0.0f);
   background_->Show();
   ui::ScopedLayerAnimationSettings settings(
       background_->GetNativeView()->layer()->GetAnimator());
   background_->GetNativeView()->layer()->SetOpacity(kBackdropOpacity);
 }
 
 }  // namespace internal
 }  // namespace ash