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

ash/common/system/overview/overview_button_tray.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ASH_COMMON_SYSTEM_OVERVIEW_OVERVIEW_BUTTON_TRAY_H_
 #define ASH_COMMON_SYSTEM_OVERVIEW_OVERVIEW_BUTTON_TRAY_H_
 
 #include "ash/ash_export.h"
 #include "ash/common/session/session_state_observer.h"
 #include "ash/common/shell_observer.h"
 #include "ash/common/system/tray/tray_background_view.h"
 #include "base/macros.h"
 
 namespace views {
 class ImageView;
 }
 
 namespace ash {
+class ViewObserver;
 
 // Status area tray for showing a toggle for Overview Mode. Overview Mode
 // is equivalent to WindowSelectorController being in selection mode.
 // This hosts a ShellObserver that listens for the activation of Maximize Mode
 // This tray will only be visible while in this state. This tray does not
 // provide any bubble view windows.
 class ASH_EXPORT OverviewButtonTray : public TrayBackgroundView,
                                       public SessionStateObserver,
                                       public ShellObserver {
  public:
-  explicit OverviewButtonTray(WmShelf* wm_shelf);
+  explicit OverviewButtonTray(WmShelf* wm_shelf, ViewObserver* view_observer);
   ~OverviewButtonTray() override;
 
   // Updates the tray's visibility based on the LoginStatus and the current
   // state of MaximizeMode
   virtual void UpdateAfterLoginStatusChange(LoginStatus status);
 
   // ActionableView:
   bool PerformAction(const ui::Event& event) override;
 
   // SessionStateObserver:
@@ skipping 10 matching lines @@
   void HideBubbleWithView(const views::TrayBubbleView* bubble_view) override;
   void SetShelfAlignment(ShelfAlignment alignment) override;
 
  private:
   friend class OverviewButtonTrayTest;
 
   // Creates a new border for the icon. The padding is determined based on the
   // alignment of the shelf.
   void SetIconBorderForShelfAlignment();
 
+  // Sets an empty border around the overview tray to change user-visible size
+  // of the dark background. Doesn't do anything in MD.
+  void SetOverviewTrayBorder();
+
   // Sets the icon to visible if maximize mode is enabled and
   // WindowSelectorController::CanSelect.
   void UpdateIconVisibility();
 
   // Weak pointer, will be parented by TrayContainer for its lifetime.
   views::ImageView* icon_;
 
   DISALLOW_COPY_AND_ASSIGN(OverviewButtonTray);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_OVERVIEW_OVERVIEW_BUTTON_TRAY_H_