ash: Reorder shutdown of ShelfLayoutManager and StatusAreaWidget

ash/shelf/shelf_widget.cc

Index: ash/shelf/shelf_widget.cc
diff --git a/ash/shelf/shelf_widget.cc b/ash/shelf/shelf_widget.cc
index 216b0901d32855775fe45832886cfcc803346162..601cecdfc73ed72ca7806716a6b4508f651afc02 100644
--- a/ash/shelf/shelf_widget.cc
+++ b/ash/shelf/shelf_widget.cc
@@ -751,12 +751,17 @@ FocusCycler* ShelfWidget::GetFocusCycler() {
   return delegate_view_->focus_cycler();
 }
 
-void ShelfWidget::ShutdownStatusAreaWidget() {
+void ShelfWidget::Shutdown() {
+  // Shutting down the status area widget may cause other widgets (e.g. bubbles)
+  // to close, so uninstall the ShelfLayoutManager event filters first.
+  if (shelf_layout_manager_)
+    shelf_layout_manager_->PrepareForShutdown();

[oshima, 2016/05/24 20:49:10]

can you also add comment why we shouldn't remove the shelf layout manager's
observer here?

[James Cook, 2016/05/24 21:18:14]

Good catch! Actually, if we reset the shelf_layout_manager_ pointer here we
don't need to be a ShelfLayoutManagerObserver at all!

+
   if (status_area_widget_) {
     Shell::GetInstance()->focus_cycler()->RemoveWidget(status_area_widget_);
     status_area_widget_->Shutdown();
+    status_area_widget_ = nullptr;
   }
-  status_area_widget_ = NULL;
 }
 
 void ShelfWidget::ForceUndimming(bool force) {