Introduce a type of View background that stays in sync with its host

ash/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/system/tray/system_tray.h"
 
 #include <algorithm>
 #include <map>
 #include <vector>
 
@@ skipping 478 matching lines @@
     full_system_tray_menu_ = items.size() > 1;
 
     TrayBubbleView::InitParams init_params(
         GetAnchorAlignment(), kTrayMenuMinimumWidth, kTrayPopupMaxWidth);
     // TODO(oshima): Change TrayBubbleView itself.
     init_params.can_activate = false;
     if (detailed) {
       // This is the case where a volume control or brightness control bubble
       // is created.
       init_params.max_height = default_bubble_height_;
-      init_params.bg_color = kBackgroundColor;
     } else {
       init_params.bg_color = kHeaderBackgroundColor;
     }
     if (bubble_type == SystemTrayBubble::BUBBLE_TYPE_DEFAULT)
       init_params.close_on_deactivate = !persistent;
     SystemTrayBubble* bubble = new SystemTrayBubble(this, items, bubble_type);
 
     system_bubble_.reset(new SystemBubbleWrapper(bubble));
     system_bubble_->InitView(this, GetBubbleAnchor(), GetBubbleAnchorInsets(),
                              &init_params, persistent);
@@ skipping 233 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