Harmony - Use FocusableBorder for comboboxes on Mac

ui/views/style/platform_style_mac.mm

Index: ui/views/style/platform_style_mac.mm
diff --git a/ui/views/style/platform_style_mac.mm b/ui/views/style/platform_style_mac.mm
index 866bba64424ff4c8a7f9876c0567c8dbd7287280..879626e4e3a004cb360e6368e04f82d8d0f0a38f 100644
--- a/ui/views/style/platform_style_mac.mm
+++ b/ui/views/style/platform_style_mac.mm
@@ -53,12 +53,6 @@ std::unique_ptr<FocusableBorder> PlatformStyle::CreateComboboxBorder() {
 }
 
 // static
-std::unique_ptr<Background> PlatformStyle::CreateComboboxBackground(
-    int shoulder_width) {
-  return base::MakeUnique<ComboboxBackgroundMac>(shoulder_width);
-}
-
-// static
 std::unique_ptr<ScrollBar> PlatformStyle::CreateScrollBar(bool is_horizontal) {
   return base::MakeUnique<CocoaScrollBar>(is_horizontal);
 }