Keep dedicated layers for hiding animation

ui/wm/core/window_animations.h

Index: ui/wm/core/window_animations.h
diff --git a/ui/wm/core/window_animations.h b/ui/wm/core/window_animations.h
index 2c7997d9538a647ba306e278cd304a1ab8905ba3..e3805f53535fd135302fabedaee270c6895ef8cf 100644
--- a/ui/wm/core/window_animations.h
+++ b/ui/wm/core/window_animations.h
@@ -7,6 +7,7 @@
 
 #include <vector>
 
+#include "ui/compositor/scoped_layer_animation_settings.h"
 #include "ui/wm/core/wm_core_export.h"
 
 namespace aura {
@@ -81,12 +82,37 @@ WM_CORE_EXPORT void SetWindowVisibilityAnimationVerticalPosition(
     aura::Window* window,
     float position);
 
-// Creates an ImplicitAnimationObserver that takes ownership of the layers
-// associated with a Window so that the animation can continue after the Window
-// has been destroyed.
-// The returned object deletes itself when the animations are done.
-WM_CORE_EXPORT ui::ImplicitAnimationObserver*
-    CreateHidingWindowAnimationObserver(aura::Window* window);
+// A wrapper of ui::ScopedLayerAnimationSettings for hiding animations.
+// Use this to ensure that the animation is visible even after
+// the window is deleted, instead of directly using
+// ui::ScopedLayerAnimationSettings.
+class WM_CORE_EXPORT ScopedHidingAnimationSettings {
+ public:
+  explicit ScopedHidingAnimationSettings(aura::Window* window);
+  ~ScopedHidingAnimationSettings();
+
+  // Returns the wrapped ScopedLayeAnimationSettings instance.
+  ui::ScopedLayerAnimationSettings* layer_animation_settings() {
+    return &layer_animation_settings_;
+  }
+
+  // When set to true, this recreates layers for the window and and puts

[sky, 2014/03/13 21:09:37]

Document when you would want to do this.
Can you pass this to the constructor instead of a setter?

[oshima, 2014/03/13 22:03:16]

I added an example. 
It thought about it but I preferred this way because it's better than the
following IMHO.

ScopedHidingAnimationSettings(
   window,
   ture /* ensure visible after focus lost */);
        

[sky, 2014/03/13 22:04:05]

Then add an enum.

+  // the original (and animating) layers on top of the |window_| and

[sky, 2014/03/13 21:09:37]

'the |window_|' -> |window_|

[oshima, 2014/03/13 22:03:16]

Done.

+  // its transient children so that these layers stay above new
+  // focused window.
+  // Note that this is effective only if the |window| has a focus when

[sky, 2014/03/13 21:09:37]

'a focus' -> focus

[oshima, 2014/03/13 22:03:16]

Done.

+  // applying the animation.
+  void set_ensure_visible_after_focus_lost(bool value) {
+    ensure_visibility_after_focus_lost_ = value;

[sky, 2014/03/13 21:09:37]

Make field and method name match here.

[oshima, 2014/03/13 22:03:16]

Done.

+  }
+
+ private:
+  aura::Window* window_;
+  bool ensure_visibility_after_focus_lost_;
+  ui::ScopedLayerAnimationSettings layer_animation_settings_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedHidingAnimationSettings);
+};
 
 // Returns false if the |window| didn't animate.
 WM_CORE_EXPORT bool AnimateOnChildWindowVisibilityChanged(aura::Window* window,