Fix white flash when user sings out and wallpaper animation regression

ash/root_window_controller.cc

Index: ash/root_window_controller.cc
diff --git a/ash/root_window_controller.cc b/ash/root_window_controller.cc
index cfc82acacb128cd2217cd95e60e1480af7368765..15fba6b576d0d02381e576ad0bd48c6d49d53f1a 100644
--- a/ash/root_window_controller.cc
+++ b/ash/root_window_controller.cc
@@ -287,6 +287,8 @@ void RootWindowController::CloseChildWindows() {
   // Close background widget first as it depends on tooltip.
   root_window_->SetProperty(kWindowDesktopComponent,
       static_cast<DesktopBackgroundWidgetController*>(NULL));
+  root_window_->SetProperty(kComponentWrapper,
+                            static_cast<ComponentWrapper*>(NULL));
 
   workspace_controller_.reset();
   aura::client::SetTooltipClient(root_window_.get(), NULL);