[Chrome OS MD] Draw a 1px separator between 2 tray items

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 550555f7370f7d582aeb9ba477fa5ea9079a5dcc..fd5875b176460d62d8a78fb88fb66a238a1107ba 100644
--- a/ash/common/system/status_area_widget.h
+++ b/ash/common/system/status_area_widget.h
@@ -8,6 +8,7 @@
 #include "ash/ash_export.h"
 #include "ash/common/login_status.h"
 #include "ash/common/shelf/shelf_types.h"
+#include "ash/common/system/view_observer.h"
 #include "base/macros.h"
 #include "ui/views/widget/widget.h"
 
@@ -16,6 +17,7 @@ class OverviewButtonTray;
 class ShellDelegate;
 class StatusAreaWidgetDelegate;
 class SystemTray;
+class TrayBackgroundView;
 class WebNotificationTray;
 class WmShelf;
 class WmWindow;
@@ -26,7 +28,7 @@ class PaletteTray;
 class VirtualKeyboardTray;
 #endif
 
-class ASH_EXPORT StatusAreaWidget : public views::Widget {
+class ASH_EXPORT StatusAreaWidget : public views::Widget, public ViewObserver {
  public:
   StatusAreaWidget(WmWindow* status_container, WmShelf* wm_shelf);
   ~StatusAreaWidget() override;
@@ -75,6 +77,12 @@ class ASH_EXPORT StatusAreaWidget : public views::Widget {
   void OnMouseEvent(ui::MouseEvent* event) override;
   void OnGestureEvent(ui::GestureEvent* event) override;
 
+  // Based on visibility of |tray| and tray item on its right, it sets |tray|'s
+  // visibility of the separator either to true or false. Note that no leading
+  // separator is required before the |logout_button_tray_| because that
+  // button's red background is distinctive on its own.
+  void OnVisibilityChange(TrayBackgroundView* tray) override;
+
  private:
   void AddSystemTray();
   void AddWebNotificationTray();