Use MD-style focus indicator on DL shelf items.

ui/views/controls/button/custom_button.h

Index: ui/views/controls/button/custom_button.h
diff --git a/ui/views/controls/button/custom_button.h b/ui/views/controls/button/custom_button.h
index d91d3e68771cd9ec6ec873891541b048ec1437a2..05840e0b2dd7a2463c78a0f35a1605990b89e43f 100644
--- a/ui/views/controls/button/custom_button.h
+++ b/ui/views/controls/button/custom_button.h
@@ -32,8 +32,11 @@ class VIEWS_EXPORT CustomButton : public Button, public gfx::AnimationDelegate {
   // The menu button's class name.
   static const char kViewClassName[];
 
-  static const CustomButton* AsCustomButton(const views::View* view);
-  static CustomButton* AsCustomButton(views::View* view);
+  static const CustomButton* AsCustomButton(const View* view);
+  static CustomButton* AsCustomButton(View* view);
+
+  // Paint an MD-style focus ring on the given canvas at the given bounds.
+  static void PaintMdFocusRing(gfx::Canvas* canvas, View* view);
 
   ~CustomButton() override;