Fix a leak in wm::AnimateOnChildWindowVisibilityChanged().

ui/wm/core/window_animations.cc

Index: ui/wm/core/window_animations.cc
diff --git a/ui/wm/core/window_animations.cc b/ui/wm/core/window_animations.cc
index a79db3a15d6c45a76d6cdb78a8e3e7dc2db5035a..ff0184af0e6805156392b1d1a17c62206b51e410 100644
--- a/ui/wm/core/window_animations.cc
+++ b/ui/wm/core/window_animations.cc
@@ -119,7 +119,6 @@ class HidingWindowAnimationObserverBase : public aura::WindowObserver {
           aura::client::GetAnimationHost(window_);
       if (animation_host)
         animation_host->OnWindowHidingAnimationCompleted();
-      window_->RemoveObserver(this);
     }
     delete this;
   }
@@ -128,9 +127,7 @@ class HidingWindowAnimationObserverBase : public aura::WindowObserver {
   // Invoked when the window is destroyed (or destroying).
   void WindowInvalid() {
     layer_owner_->root()->SuppressPaint();
-
-    window_->RemoveObserver(this);
-    window_ = NULL;
+    delete this;
   }
 
   aura::Window* window_;