Remove aura::RootWindow instance from LayerAnimator::observers_ when the window is deleted

ui/aura/root_window.cc

Index: ui/aura/root_window.cc
diff --git a/ui/aura/root_window.cc b/ui/aura/root_window.cc
index bf646fcf0b0d279513965db3f1347098ab8e5d13..48d2798693f08439b1bbd2de22737fcfa6cab4f4 100644
--- a/ui/aura/root_window.cc
+++ b/ui/aura/root_window.cc
@@ -434,6 +434,8 @@ RootWindow::~RootWindow() {
   // Make sure to destroy the compositor before terminating so that state is
   // cleared and we don't hit asserts.
   compositor_ = NULL;
+  // An observer may have been added by an animation on the RootWindow.
+  layer()->GetAnimator()->RemoveObserver(this);
 #ifdef USE_WEBKIT_COMPOSITOR
   if (!ui::Compositor::compositor_factory())
     ui::CompositorCC::Terminate();