MacViews: draw combobox arrow backgrounds

ui/views/controls/focusable_rounded_border_mac.cc

 // 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.
 
 #include "ui/views/controls/focusable_rounded_border_mac.h"
 
 #include "ui/gfx/canvas.h"
+#include "ui/native_theme/native_theme_mac.h"
 
 namespace {
 
 const int kThickness = 1;
-const int kCornerRadius = 5;
 
 }  // namespace
 
 namespace views {
 
 FocusableRoundedBorder::FocusableRoundedBorder() {
   // TODO(ellyjones): These insets seem like they shouldn't be big enough, but
   // they are, and insetting by corner_radius_ instead produces gargantuan
   // padding. Why is that?
   SetInsets(kThickness, kThickness, kThickness, kThickness);
 }
 
 FocusableRoundedBorder::~FocusableRoundedBorder() {}
 
 // For now, this is similar to RoundedRectBorder::Paint(), but this method will
 // likely diverge in future.
 // TODO(ellyjones): Diverge it by adding soft focus rings.
 void FocusableRoundedBorder::Paint(const View& view, gfx::Canvas* canvas) {
   SkPaint paint;
   paint.setStyle(SkPaint::kStroke_Style);
   paint.setStrokeWidth(kThickness);
   paint.setColor(GetCurrentColor(view));
   paint.setAntiAlias(true);
 
   float half_thickness = kThickness / 2.0f;
   gfx::RectF bounds(view.GetLocalBounds());
   bounds.Inset(half_thickness, half_thickness);
-  canvas->DrawRoundRect(bounds, kCornerRadius, paint);
+  canvas->DrawRoundRect(bounds, ui::NativeThemeMac::kComboboxCornerRadius,
+                        paint);
 }
 
 }  // namespace views