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

ui/views/controls/focus_ring.h

+// Copyright 2016 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_FOCUS_RING_H_
+#define UI_VIEWS_CONTROLS_FOCUS_RING_H_
+
+#include "ui/views/view.h"
+
+namespace views {
+
+// FocusRing is a View that is designed to act as an indicator of focus for its
+// parent. It is a stand-alone view that paints to a layer which extends beyond
+// the bounds of its parent view.
+class FocusRing : public View {
+ public:
+  // Create a FocusRing and adds it to |parent|.
+  static void Install(views::View* parent);
+
+  // Removes the FocusRing from |parent|.
+  static void Uninstall(views::View* parent);
+
+  // View:
+  const char* GetClassName() const override;
+  bool CanProcessEventsWithinSubtree() const override;
+  void Layout() override;
+  void OnPaint(gfx::Canvas* canvas) override;
+
+ private:
+  static const char kViewClassName[];
+
+  FocusRing();
+  ~FocusRing() override;
+
+  DISALLOW_COPY_AND_ASSIGN(FocusRing);
+};
+
+}  // views
+
+#endif  // UI_VIEWS_CONTROLS_FOCUS_RING_H_