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

ash/common/system/tray/system_tray.h

Index: ash/common/system/tray/system_tray.h
diff --git a/ash/common/system/tray/system_tray.h b/ash/common/system/tray/system_tray.h
index 9029cb16f70f1bdc8e728bd069cfb97fd7b382cf..a5fb6532b71c66a818ebe5fe46bc2837bbb04d24 100644
--- a/ash/common/system/tray/system_tray.h
+++ b/ash/common/system/tray/system_tray.h
@@ -29,6 +29,7 @@ class TrayCast;
 class TrayDate;
 class TrayUpdate;
 class TrayUser;
+class ViewObserver;
 class WebNotificationTray;
 
 // There are different methods for creating bubble views.
@@ -40,7 +41,7 @@ enum BubbleCreationType {
 class ASH_EXPORT SystemTray : public TrayBackgroundView,
                               public views::TrayBubbleView::Delegate {
  public:
-  explicit SystemTray(WmShelf* wm_shelf);
+  explicit SystemTray(WmShelf* wm_shelf, ViewObserver* view_observer);
   ~SystemTray() override;
 
   // Calls TrayBackgroundView::Initialize(), creates the tray items, and
@@ -212,6 +213,10 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
 
   const ScopedVector<SystemTrayItem>& items() const { return items_; }
 
+  // Sets an empty border around the system tray to change user-visible size
+  // of the dark background. Doesn't do anything in MD.
+  void AdjustStatusTrayBackground();
+
   // Overridden from ActionableView.
   bool PerformAction(const ui::Event& event) override;