[ash-md] Animates overview shield in and out

ash/common/wm/overview/cleanup_animation_observer.cc

+// Copyright 2016 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/common/wm/overview/cleanup_animation_observer.h"
+
+#include "ui/views/widget/widget.h"
+
+namespace ash {
+
+CleanupAnimationObserver::CleanupAnimationObserver(
+    std::unique_ptr<views::Widget> widget)
+    : widget_(std::move(widget)), owner_(nullptr) {
+  DCHECK(widget_);
+}
+
+CleanupAnimationObserver::~CleanupAnimationObserver() {}
+
+void CleanupAnimationObserver::OnImplicitAnimationsCompleted() {
+  // |widget_| may get reset if Shutdown() is called prior to this method.
+  if (!widget_)
+    return;
+  if (owner_) {
+    owner_->RemoveAndDestroyAnimationObserver(this);
+    return;
+  }
+  delete this;
+}
+
+void CleanupAnimationObserver::SetOwner(WindowSelectorDelegate* owner) {
+  owner_ = owner;
+}
+
+void CleanupAnimationObserver::Shutdown() {
+  widget_.reset();
+  owner_ = nullptr;
+}
+
+}  // namespace ash