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

ui/views/bubble/tray_bubble_view.h

 // 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.
 
 #ifndef UI_VIEWS_BUBBLE_TRAY_BUBBLE_VIEW_H_
 #define UI_VIEWS_BUBBLE_TRAY_BUBBLE_VIEW_H_
 
 #include <memory>
 
 #include "base/macros.h"
+#include "base/optional.h"
 #include "ui/views/bubble/bubble_dialog_delegate.h"
 #include "ui/views/mouse_watcher.h"
 #include "ui/views/views_export.h"
 
 namespace views {
 class BoxLayout;
 class View;
 class Widget;
 }
 
@@ skipping 55 matching lines @@
 
   struct VIEWS_EXPORT InitParams {
     InitParams(AnchorAlignment anchor_alignment, int min_width, int max_width);
     InitParams(const InitParams& other);
     AnchorAlignment anchor_alignment;
     int min_width;
     int max_width;
     int max_height;
     bool can_activate;
     bool close_on_deactivate;
-    SkColor bg_color;
+    // If not provided, the bg color will be derived from the NativeTheme.
+    base::Optional<SkColor> bg_color;
   };
 
   // Constructs and returns a TrayBubbleView. |init_params| may be modified.
   static TrayBubbleView* Create(views::View* anchor,
                                 Delegate* delegate,
                                 InitParams* init_params);
 
   ~TrayBubbleView() override;
 
   // Sets up animations, and show the bubble. Must occur after CreateBubble()
@@ skipping 76 matching lines @@
 
   // Used to find any mouse movements.
   std::unique_ptr<MouseWatcher> mouse_watcher_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayBubbleView);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_BUBBLE_TRAY_BUBBLE_VIEW_H_