Fix Chrome crashes on calling OnTrayVisibilityChange

ash/common/system/status_area_widget.h

Index: ash/common/system/status_area_widget.h
diff --git a/ash/common/system/status_area_widget.h b/ash/common/system/status_area_widget.h
index bc74b20277ab332350f89629e2edea323cc69e36..be9b9a07b6dad65a527ae540689b08c3e346c0af 100644
--- a/ash/common/system/status_area_widget.h
+++ b/ash/common/system/status_area_widget.h
@@ -27,6 +27,10 @@ class PaletteTray;
 class VirtualKeyboardTray;
 #endif
 
+namespace test {
+class SystemTrayTest;
+}
+
 class ASH_EXPORT StatusAreaWidget : public views::Widget,
                                     public ShelfBackgroundAnimatorObserver {
  public:
@@ -93,6 +97,8 @@ class ASH_EXPORT StatusAreaWidget : public views::Widget,
   void UpdateShelfItemBackground(int alpha) override;
 
  private:
+  friend class test::SystemTrayTest;
+
   void AddSystemTray();
   void AddWebNotificationTray();
 #if defined(OS_CHROMEOS)
@@ -122,6 +128,9 @@ class ASH_EXPORT StatusAreaWidget : public views::Widget,
 
   WmShelf* wm_shelf_;
 
+  // Indicates whether all tray items have been successfully initialized.
+  bool is_initialized_;
+
   DISALLOW_COPY_AND_ASSIGN(StatusAreaWidget);
 };