[ash-md] Fixes clipping of controls in system tray

ash/common/system/tray/tray_details_view.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/tray_details_view.h"
 
 #include "ash/common/ash_view_ids.h"
 #include "ash/common/material_design/material_design_controller.h"
 #include "ash/common/system/tray/fixed_sized_scroll_view.h"
 #include "ash/common/system/tray/system_tray.h"
@@ skipping 304 matching lines @@
     back_button_ = title_row_->AddBackButton(this);
 
   Layout();
 }
 
 void TrayDetailsView::CreateScrollableList() {
   DCHECK(!scroller_);
   scroll_content_ = new ScrollContentsView();
   scroller_ = new FixedSizedScrollView;
   scroller_->SetContentsView(scroll_content_);
+  // Make the |scroller_| have a layer to clip |scroll_content_|'s children.
+  // TODO(varkha): Make the sticky rows work with EnableViewPortLayer().
+  scroller_->SetPaintToLayer(true);
+  scroller_->set_background(
+      views::Background::CreateSolidBackground(kBackgroundColor));
+  scroller_->layer()->SetMasksToBounds(true);
 
   // Note: |scroller_| takes ownership of |scroll_border_|.
   if (!UseMd()) {
     // In MD, the scroller is always the last thing, so this border is
     // unnecessary and reserves extra space we don't want.
     scroll_border_ = new ScrollBorder;
     scroller_->SetBorder(std::unique_ptr<views::Border>(scroll_border_));
   }
 
   AddChildView(scroller_);
@@ skipping 110 matching lines @@
     if (index < child_count() - 1 && child_at(index + 1) != title_row_)
       scroll_border_->set_visible(true);
     else
       scroll_border_->set_visible(false);
   }
 
   views::View::OnPaintBorder(canvas);
 }
 
 }  // namespace ash