Keep dedicated layers for hiding animation

ui/views/corewm/window_animations.cc

Index: ui/views/corewm/window_animations.cc
diff --git a/ui/views/corewm/window_animations.cc b/ui/views/corewm/window_animations.cc
index 4eb2caeceaf1ad2054890b00bd36f4a765c35840..b2e255fde3765d39489bc43ca48b461a6a1e85ba 100644
--- a/ui/views/corewm/window_animations.cc
+++ b/ui/views/corewm/window_animations.cc
@@ -109,6 +109,11 @@ int GetWindowVisibilityAnimationType(aura::Window* window) {
   return type;
 }
 
+class HidingWindowAnimationObserver;
+DEFINE_WINDOW_PROPERTY_KEY(HidingWindowAnimationObserver*,
+                           kHidingWindowAnimationObserverKey,
+                           NULL);
+
 // Observes a hide animation.
 // A window can be hidden for a variety of reasons. Sometimes, Hide() will be
 // called and life is simple. Sometimes, the window is actually bound to a
@@ -125,13 +130,24 @@ class HidingWindowAnimationObserver : public ui::ImplicitAnimationObserver,
                                       public aura::WindowObserver {
  public:
   explicit HidingWindowAnimationObserver(aura::Window* window)
-      : window_(window) {
+      : window_(window),
+        layers_detached_(false) {
     window_->AddObserver(this);
+    window->SetProperty(kHidingWindowAnimationObserverKey, this);
   }
   virtual ~HidingWindowAnimationObserver() {
     STLDeleteElements(&layers_);
   }
 
+  ui::Layer* DetachAndRecreateLayers() {
+    ui::Layer* old_layer = views::corewm::RecreateWindowLayers(window_, true);
+    // Make the new layer unvisible immediately.
+    window_->layer()->SetVisible(false);
+    layers_.push_back(old_layer);
+    layers_detached_ = true;
+    return old_layer;
+  }
+
  private:
   // Overridden from ui::ImplicitAnimationObserver:
   virtual void OnImplicitAnimationsCompleted() OVERRIDE {
@@ -142,6 +158,7 @@ class HidingWindowAnimationObserver : public ui::ImplicitAnimationObserver,
       if (animation_host)
         animation_host->OnWindowHidingAnimationCompleted();
       window_->RemoveObserver(this);
+      window_->ClearProperty(kHidingWindowAnimationObserverKey);
     }
     delete this;
   }
@@ -149,15 +166,16 @@ class HidingWindowAnimationObserver : public ui::ImplicitAnimationObserver,
   // Overridden from aura::WindowObserver:
   virtual void OnWindowDestroying(aura::Window* window) OVERRIDE {
     DCHECK_EQ(window, window_);
-    DCHECK(layers_.empty());
-    AcquireAllLayers(window_);
-
-    // If the Widget has views with layers, then it is necessary to take
-    // ownership of those layers too.
-    views::Widget* widget = views::Widget::GetWidgetForNativeWindow(window_);
-    const views::Widget* const_widget = widget;
-    if (widget && const_widget->GetRootView() && widget->GetContentsView())
-      AcquireAllViewLayers(widget->GetContentsView());
+    DCHECK(layers_.empty() || layers_detached_);
+    if (!layers_detached_) {
+      AcquireAllLayers(window_);
+      // If the Widget has views with layers, then it is necessary to take
+      // ownership of those layers too.
+      views::Widget* widget = views::Widget::GetWidgetForNativeWindow(window_);
+      const views::Widget* const_widget = widget;
+      if (widget && const_widget->GetRootView() && widget->GetContentsView())
+        AcquireAllViewLayers(widget->GetContentsView());
+    }
     window_->RemoveObserver(this);
     window_ = NULL;
   }
@@ -186,6 +204,7 @@ class HidingWindowAnimationObserver : public ui::ImplicitAnimationObserver,
 
   aura::Window* window_;
   std::vector<ui::Layer*> layers_;
+  bool layers_detached_;
 
   DISALLOW_COPY_AND_ASSIGN(HidingWindowAnimationObserver);
 };
@@ -546,6 +565,12 @@ ui::ImplicitAnimationObserver* CreateHidingWindowAnimationObserver(
   return new HidingWindowAnimationObserver(window);
 }
 
+ui::Layer* DetachHidingAnimationLayer(aura::Window* window) {
+  HidingWindowAnimationObserver* observer =
+      window->GetProperty(kHidingWindowAnimationObserverKey);
+  return observer ? observer->DetachAndRecreateLayers() : NULL;
+}
+
 bool AnimateOnChildWindowVisibilityChanged(aura::Window* window, bool visible) {
   if (WindowAnimationsDisabled(window))
     return false;