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

ui/views/controls/textfield/textfield.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_TEXTFIELD_TEXTFIELD_H_
 #define UI_VIEWS_CONTROLS_TEXTFIELD_TEXTFIELD_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 490 matching lines @@
   int drag_start_display_offset_;
 
   // Tracks if touch editing handles are hidden because user has started
   // scrolling. If |true|, handles are shown after scrolling ends.
   bool touch_handles_hidden_due_to_scroll_;
 
   // Context menu related members.
   std::unique_ptr<ui::SimpleMenuModel> context_menu_contents_;
   std::unique_ptr<views::MenuRunner> context_menu_runner_;
 
+  // A child that indicates focus.
+  View* focus_ring_;
+
   // Used to bind callback functions to this object.
   base::WeakPtrFactory<Textfield> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Textfield);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_TEXTFIELD_TEXTFIELD_H_