Refactor MdFocusRing to make it easier to reuse on other controls.

ui/views/controls/combobox/combobox.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_CONTROLS_COMBOBOX_COMBOBOX_H_
 #define UI_VIEWS_CONTROLS_COMBOBOX_COMBOBOX_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/strings/string16.h"
@@ skipping 191 matching lines @@
 
   // The transparent buttons to handle events and render buttons. These are
   // placed on top of this combobox as child views, accept event and manage the
   // button states. These are not rendered but when |style_| is
   // STYLE_NOTIFY_ON_CLICK, a Combobox renders the button images according to
   // these button states.
   // The base View takes the ownerships of these as child views.
   CustomButton* text_button_;
   CustomButton* arrow_button_;
 
+  // A child that indicates focus.
+  View* focus_ring_;
+
   // Set while the dropdown is showing. Ensures the menu is closed if |this| is
   // destroyed.
   std::unique_ptr<MenuModelAdapter> menu_model_adapter_;
   std::unique_ptr<MenuRunner> menu_runner_;
 
   // The image to be drawn for this combobox's arrow.
   gfx::ImageSkia arrow_image_;
 
   // When true, the size of contents is defined by the selected label.
   // Otherwise, it's defined by the widest label in the menu. If this is set to
   // true, the parent view must relayout in ChildPreferredSizeChanged().
   bool size_to_largest_label_;
 
   // Used for making calbacks.
   base::WeakPtrFactory<Combobox> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Combobox);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_COMBOBOX_COMBOBOX_H_