Remove the extra separator appears on the right side of the shelf

ash/common/system/tray/system_tray.cc

 // Copyright (c) 2012 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.
 
 #include "ash/common/system/tray/system_tray.h"
 
 #include <algorithm>
 #include <map>
 #include <vector>
 
@@ skipping 203 matching lines @@
       tray_date_(nullptr),
       tray_network_(nullptr),
       tray_tiles_(nullptr),
       tray_system_info_(nullptr),
       tray_update_(nullptr),
       screen_capture_tray_item_(nullptr),
       screen_share_tray_item_(nullptr) {
   if (MaterialDesignController::IsShelfMaterial()) {
     SetInkDropMode(InkDropMode::ON);
     SetContentsBackground(false);
+
+    // Since |system_tray| locates on the right most position, no separator is
+    // required on its right side.
+    set_separator_visibility(false);
   } else {
     SetContentsBackground(true);
   }
 }
 
 SystemTray::~SystemTray() {
   // Destroy any child views that might have back pointers before ~View().
   activation_observer_.reset();
   key_event_watcher_.reset();
   system_bubble_.reset();
@@ skipping 661 matching lines @@
           .work_area()
           .height();
   if (work_area_height > 0) {
     UMA_HISTOGRAM_CUSTOM_COUNTS(
         "Ash.SystemMenu.PercentageOfWorkAreaHeightCoveredByMenu",
         100 * bubble_view->height() / work_area_height, 1, 300, 100);
   }
 }
 
 }  // namespace ash