Reuse NativeThemeAuraDark for cros tray.

ash/common/system/tray/tray_background_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_background_view.h"
 
 #include "ash/common/material_design/material_design_controller.h"
 #include "ash/common/shelf/shelf_constants.h"
 #include "ash/common/shelf/wm_shelf.h"
 #include "ash/common/shelf/wm_shelf_util.h"
@@ skipping 12 matching lines @@
 #include "ui/compositor/scoped_layer_animation_settings.h"
 #include "ui/events/event_constants.h"
 #include "ui/gfx/animation/tween.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/gfx/image/image_skia_operations.h"
 #include "ui/gfx/nine_image_painter.h"
 #include "ui/gfx/skia_util.h"
 #include "ui/gfx/transform.h"
+#include "ui/native_theme/native_theme_dark_aura.h"
 #include "ui/views/background.h"
 #include "ui/views/layout/box_layout.h"
 #include "ui/wm/core/window_animations.h"
 
 namespace {
 
 const int kAnimationDurationForPopupMs = 200;
 
 // Duration of opacity animation for visibility changes.
 const int kAnimationDurationForVisibilityMs = 250;
@@ skipping 270 matching lines @@
     layer()->SetOpacity(0.0f);
     layer()->SetVisible(false);
     HideTransformation();
   }
 }
 
 const char* TrayBackgroundView::GetClassName() const {
   return kViewClassName;
 }
 
+const ui::NativeTheme* TrayBackgroundView::GetNativeTheme() const {
+  return ui::NativeThemeDarkAura::instance();

[tdanderson, 2016/08/17 19:35:00]

I would prefer for this were MD-only, i.e.,

if (MaterialDesignController::IsShelfMaterial())
  return ui::NativeThemeDarkAura::instance();
return ActionableView::GetNativeTheme();

This guards against the possibility we accidentally regress something in non-MD
(not just for the system tray, but also for the other derived classes of
TrayBackgroundView).

[Evan Stade, 2016/08/18 00:38:02]

I don't think this is necessary and it's a little bit gross, but I will agree it
is safer (less likely to cause regressions), so Done.

+}
+
 void TrayBackgroundView::ChildPreferredSizeChanged(views::View* child) {
   PreferredSizeChanged();
 }
 
 void TrayBackgroundView::GetAccessibleState(ui::AXViewState* state) {
   ActionableView::GetAccessibleState(state);
   state->name = GetAccessibleNameForTray();
 }
 
 void TrayBackgroundView::AboutToRequestFocusFromTabTraversal(bool reverse) {
@@ skipping 169 matching lines @@
 }
 
 void TrayBackgroundView::UpdateShelfItemBackground(int alpha) {
   if (background_) {
     background_->set_alpha(alpha);
     SchedulePaint();
   }
 }
 
 }  // namespace ash