Refactor AddScrollListItem() in system menu detailed views

ash/system/tray/tray_details_view_unittest.cc

 // Copyright 2013 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/system/tray/tray_details_view.h"
 
 #include "ash/ash_view_ids.h"
 #include "ash/resources/grit/ash_resources.h"
 #include "ash/strings/grit/ash_strings.h"
 #include "ash/system/tray/system_tray.h"
@@ skipping 25 matching lines @@
   }
 
   ~TestDetailsView() override {}
 
   TrayPopupHeaderButton* tray_popup_header_button() {
     return tray_popup_header_button_;
   }
 
   void CreateScrollerViews() { CreateScrollableList(); }
 
+  views::View* scroll_content() const {
+    return TrayDetailsView::scroll_content();
+  }
+
  private:
   TrayPopupHeaderButton* tray_popup_header_button_;
 
   DISALLOW_COPY_AND_ASSIGN(TestDetailsView);
 };
 
 // Trivial item implementation that tracks its views for testing.
 class TestItem : public SystemTrayItem {
  public:
   TestItem()
@@ skipping 166 matching lines @@
 
   // Sticky header layer should be above the last child's layer.
   EXPECT_EQ(3u, layers.size());
   EXPECT_EQ(view3->layer(), layers[0]);
   EXPECT_EQ(view4->layer(), layers[1]);
   EXPECT_EQ(view2->layer(), layers[2]);
 }
 
 }  // namespace test
 }  // namespace ash