[ash-md] Animates overview shield in and out

ash/common/wm/overview/cleanup_animation_observer.h

Index: ash/common/wm/overview/cleanup_animation_observer.h
diff --git a/ash/common/wm/overview/cleanup_animation_observer.h b/ash/common/wm/overview/cleanup_animation_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..a3ad4ffd157f8e1adf6c32e64cc7decd1689604d
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+++ b/ash/common/wm/overview/cleanup_animation_observer.h
@@ -0,0 +1,48 @@
+// 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.
+
+#ifndef ASH_COMMON_WM_OVERVIEW_CLEANUP_ANIMATION_OBSERVER_H_
+#define ASH_COMMON_WM_OVERVIEW_CLEANUP_ANIMATION_OBSERVER_H_
+
+#include <memory>
+
+#include "ash/ash_export.h"
+#include "ash/common/wm/overview/window_selector_delegate.h"
+#include "base/macros.h"
+#include "ui/compositor/layer_animation_observer.h"
+
+namespace views {
+class Widget;
+}
+
+namespace ash {
+
+// An observer which holds onto the passed widget until the animation is
+// complete.
+class ASH_EXPORT CleanupAnimationObserver
+    : public ui::ImplicitAnimationObserver,
+      public DelayedAnimationObserver {
+ public:
+  explicit CleanupAnimationObserver(std::unique_ptr<views::Widget> widget);
+  ~CleanupAnimationObserver() override;
+
+  // ui::ImplicitAnimationObserver:
+  // TODO(varkha): Look into all cases when animations are not started such as
+  // zero-duration animations and ensure that the object lifetime is handled.
+  void OnImplicitAnimationsCompleted() override;
+
+  // DelayedAnimationObserver:
+  void SetOwner(WindowSelectorDelegate* owner) override;
+  void Shutdown() override;
+
+ private:
+  std::unique_ptr<views::Widget> widget_;
+  WindowSelectorDelegate* owner_;
+
+  DISALLOW_COPY_AND_ASSIGN(CleanupAnimationObserver);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_WM_OVERVIEW_CLEANUP_ANIMATION_OBSERVER_H_