[ash-md] Stacks child layers properly for sticky header rows

ash/common/system/tray/tray_popup_utils.cc

 // Copyright 2016 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/tray_popup_utils.h"
 
 #include "ash/common/ash_constants.h"
 #include "ash/common/ash_view_ids.h"
 #include "ash/common/material_design/material_design_controller.h"
 #include "ash/common/session/session_state_delegate.h"
@@ skipping 269 matching lines @@
   return views::Painter::CreateSolidFocusPainter(
       kFocusBorderColor, kFocusBorderThickness, gfx::InsetsF());
 }
 
 void TrayPopupUtils::ConfigureAsStickyHeader(views::View* view) {
   view->set_id(VIEW_ID_STICKY_HEADER);
   view->set_background(
       views::Background::CreateSolidBackground(kBackgroundColor));
   view->SetBorder(
       views::CreateEmptyBorder(gfx::Insets(kMenuSeparatorVerticalPadding, 0)));
+  view->SetPaintToLayer(true);
+  view->layer()->SetFillsBoundsOpaquely(false);
 }
 
 void TrayPopupUtils::ConfigureContainer(TriView::Container container,
                                         views::View* container_view) {
   container_view->SetLayoutManager(
       CreateDefaultLayoutManager(container).release());
 }
 
 views::LabelButton* TrayPopupUtils::CreateTrayPopupBorderlessButton(
     views::ButtonListener* listener,
@@ skipping 153 matching lines @@
 bool TrayPopupUtils::CanOpenWebUISettings(LoginStatus status) {
   // TODO(tdanderson): Consider moving this into WmShell, or introduce a
   // CanShowSettings() method in each delegate type that has a
   // ShowSettings() method.
   return status != LoginStatus::NOT_LOGGED_IN &&
          status != LoginStatus::LOCKED &&
          !WmShell::Get()->GetSessionStateDelegate()->IsInSecondaryLoginScreen();
 }
 
 }  // namespace ash